practical cht

8/7/2019 practical CHT

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PRACTICAL NO 1

AIM:~ To study soldering and desoldering of various components.

INTRODUCTION:Once a defective component needs to be isolated from the given faulty

equipment, it is required to remove the defective component from the PCB & all thisrequire a good practice of soldering & desoldering.

SOLDERING PROCESS:Soldering is the process of joining two or more metals at temperature below there

melting points using filler metal (solder) having melting point below 450`c. The solder

binds the metal together by chemical & physical processes. Chemically solder reactswith small part of each metal to be joined or soldered, thus forming a new compound.Physically the liquid solder alloy then enters the exposed pores of the metals. Solder oncooling solidifies and forms a continuous metallic bond. If the metals are not heatedproperly, solder will not penetrate into the metal pores. As a result solder will solidifyover the top of the pores in the metal & this result in defective joint known as coldsolder joint

.

SOLDER :Most of the soldering in electronics is done using tin lead alloy. Pure lead melts

at 327`c where as tin melts at 232`c and their mixture at 188`c when ratio of tin & leadis 60/40.

The tin lead ratio at which the solder alloy goes directly to liquid stage is called

ELECTRNONIC COMPOISITION & resultant alloy is known as EUTECTICALLOY. This alloy is generally referred to as 63/37 .The addition of antimony to thisalloy increases the strength. The tin lead alloy is drawn into hollow wire whose centre isfixed with flux. This is known as ROSIN CORE SOLDER. For general soldering 18gauge wire solder is used.

FLUXES:

The soldering process requires that the surface should be totally clear so thatmetal to metal contact can be established. Most of the metals in the air form an oxidelayer which prevents wetting. To maintain a clean surface flux is used. It dissolves

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oxides and allows good soldering. The flux will also assist in the transfer of heat fromthe soldering iron tip t the joint area. Flux is imbedded in solder (rosin core solder). It isalso available in paste or liquid form.

A flux should have the following properties:

1 It must be sufficiently active at room temperature to remove oxides.

2 It must be mobile enough to allow the solder to flow at this temperature.3 It must remove fingerprints, dirt, grease etc.

Traditionally fluxes can be grouped as:

1. Rosin based fluxes.2. Water soluble fluxes.3. Solvent removable synthetic fluxes.4. Low solid fluxes.

Of these rosin based fluxes are generally used for repair work. These consist of

rosin dissolved in some solvent.

TINNING:The component leads may get rusted during storage. It will be difficult t solder

such leaded components. Thus leads of such components or wires need to be tinned.Tinning consist of the application of the thin layer of solder to the surface of

metal which could be lead of a component or copper track on PCB.

The two chief methods are :1. Hot dip tinning.

2. Using soldering iron.

Before tinning a wire, the insulation must be removed with wire strippers. Thefirst method consists of immersing the metal surface to be tinning in to hot solder bath,after application of flux. This method is not used for repair work.

During repair or rework, tinning is done using soldering iron. First of all flux isapplied to the surface to be tinned.

SOLDERING IRONS:Soldering iron is used during soldering process to supply sufficient heat to melt

solder by transfer of heat from soldering iron tip. The tip of the soldering iron is appliedto a connection which is to be soldered.

There are generally three classes or types of soldering irons:

1. Resistive soldering irons.2. Soldering gun.3. Temperature controlled soldering gun.

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RESISTIVE SOLDERING IRON:It is cheapest soldering iron. These can not be used for precision work as heat

produced is in excess then required to melt solder. The excessive heat can be verydamaging PCB,S and semiconductor devices. This should be used in emergency andwhen used should be applied for minimum of time to prevent damage of devices due tooverheating.

This consists of a copper tip which is heated electrically by resistive coil. This tipacts a heat store and heat conductor.

SOLDERING GUNSoldering gun is used for soldering heavy wiring. It is not recommended for use

on PCBS. This operates on the principle of resistive heating of low resistance coppertip. Heavy currents flow through the copper tip. Because of the current involvedcorrosion of attachments nut will result in slow or no heating of the tip. It has triggerswitch to control the application of the a.c. power to resistive element. The working

Temperature s reached instantaneously.

TEMPERATURE CONTROLLED SOLDERING GUNThe soldering irons are most suited to maintenance purposes especially when

dealing with semiconductors components which are likely to be damaged byoverheating. This iron operates much slowly as compared to uncontrolled iron.

SELECTION OF SOLDERIONG IRON :Soldering irons are available in variety of sizes, shapes and wattages. In standard

iron, the input voltage is fixed; this resulting temperature depends on capacity of the

heating unit and size of the tip. Generally, soldering irons are selected on the basis ofthe input wattage or the tip, idling, temperature neither of these is valid criterion formatching the right to iron to the job. Ideal tip working temperature is defined as thetemperature range between appox 600 to 700 for most electronic assembly.

SOLDERING IRON TIP CLEANING:Iron plated tips should be cleaned while hot with metal brush or with cellulose

sponge (wet) and while cold with a wire brush to remove oxide film. These should notbe cleaned with files, sand paper or emery cloth.

DESOLDERING:This operation is frequently required during maintenance for replacing a

component. It consists of removal of solder from a previously soldered joint.

The following techniques are often used for this purpose.

1. USE OF DESOLDERING PUMPDesoldering pump is a mechanically operated, hand held desoldering tool,. This

tool consist of a outer shaft, piston handle and release pin and Teflon pin. It isdesigned to be held and operated in one hand. The pump can be disassembled andcleaned as required

.The step by step procedure for desoldering is:

Load the pump

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Heat the solder connected with soldering iron until solder melts.

Hold desoldering pump lightly against the melted solder.

Press the pin to vacuum solder from connection.

Reload and repeat as necessary to clean the area of solder.

2. USE OF DESOLDERING BRAID Desoldering braid is loosely woven, flux impregnated, stranded braid of copperwire. The joint to be desoldered is not heated using soldering iron. The braid (wick) isheated first. The solder is sucked into the braid due to capillary action when it is broughtnear joint. The used portion is cut and thrown away. In this method soldering iron nevertouches the solder so prevents over heating of components.

3. USE OF DESOLDERING BULBThis also operates on vacuum principle. The rubber is simply a hollow rubber

ball with heat resistant Teflon tip. It can be used with any soldering iron.

The iron is held in one hand and used to melt the solder. The bulb held in second handis then squeezed to create vacuum. The tip is next applied to the reheated solder.Connection action that sucks the solder up through hollow tip into bulb.

4. USE OF DESOLDERING TIP AND DIP EXTRACTORThis method is used for desoldering ICS. Here clips of the extractor are fixed

over the chip and DIP chip is applied at the other side of the PCB. All connection willmelt simultaneously. As the extractor is spring loaded , the IC chip will automaticallycome up once the solder melts.

SOLDERING DEFECTS:The defects can be classified according to their nature into major or minor

defects.Some of the defects encountered during soldering are:

DEWETTING- It occurs due to contaminated base metal surface. Dewetting ofsolder film as water on greasy surface.

PARTIAL WETTING- This is due to incomplete coverage of the surface bysolder film. This is usually a result of an inadequate time temperature cycle or ofinsufficient flux activity.

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OTHER SOLDERING DEFECTS MAY OCCUR DURING

SOLDERING PROCESS ARE:

EXCESS SOLDER

ICICLES

BRIDGING

POROSITY

OVER HEATED JOINTS

COMPONENT PREPRATION AND MOUNTING.Components are generally on one side of PCB. In double sided PCBs, the

component are generally mounted usually opposite to the major conductor patternside depending upon design.

Before mounting any component it is essential to clean the surface to besoldered with some braided cleaning tool. Component leads are bent so that

component properly fit into the circuit. Bending of component should be done withminimum stress. The bent leads should fit into the holes perpendicular to the board.

Horizontally mounted components should touch the board surface to avoidlifting of solder joint.

Vertically mounted components should not be flush to the board to avoidstrain on solder joint.

Sealed components should be mounted in such a way to provide a certaindistance from the board as insulation coating on component is extended to a certainlength along the leads.

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PRACTICAL NO 2

AIM: To check and measure various power supply voltages of pc.

Theory:The PC power supply is primarily designed simply to take AC from the

wall outlet & convert into the much lower DC voltages needed by the system.When system shut down, it must prevent any voltage overshoot & fluctuations sothat none of sensitive circuits are exposed to any damaging voltage fluctuation .Itmust include some way of providing cooling air flow, because of the conversionprocess always has some heat by product.

Converting AC to DC power:The switching mode power supply used in a PC is much lighter & more

efficient then the more common linear mode power supplies. Often used in the pastsystems, & therefore is a good choice for a power supply. The first part of PCswitching power supply is rectifier. Next is the switches circuit which chops up.the input voltage at a frequency much higher than the AC supply. Further more,any load fluctuation are fed back to the input in such away as to cause switchercircuit to adjust the input power to the transformer so that it can maintain theoutput voltage to final regulator. The switcher circuitry it self generate EMI, which

can feed back into the building AC power & contribute to problems elsewhere.

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Output voltage supply voltage lines:The voltages delivered by the power supply to the motherboard must

remain stable in spite of a wide range of input AC voltage and varying loadconditions

+5 volt supply:This is the basic supply voltage for nearly all-electronic components. The

5V supply is now sometimes used by motors, but usually only in smaller drives,such as 2.5inch & some 3.5inch drive. The +5V supply wires should always bered in any standard PC system.If regulated voltage is adjustable, the jumpers orswitches will probably be found near regulator circuit.

+12V power supply:

This line supplies most if not all, motors in the system, from drive motorto cooling fans. Because motors often used up to 50% more power on start up thenwhile running ,the +12V supply may show adequate operation while running , butbe in an over loaded condition during the 5 seconds or so immediately .after thesystem or a particular drive is turned on .

-12 V power supply:This supply line is usually used for some of the same communications

circuits that use +12 V line.

-5 V power supply:This voltage is no longer used by any device and is retained only the

purpose of backward compatibility with the older ISA slots. Originally, thisvoltage was used by some DRAM memory chips in original PC design. Microchannel system omitted this voltage from the power supply entirely

+3.3V power supply:Starting with the ATX designed in 1995 any system with ATX compatible

power supplies include a 3.3 volt supply line from the power supply to themotherboard. Currently most CPUs & DRAM used 3.3V as well as some PCI

adapter cards.

Power Supply Control Signals:Although the primary function of the power supply is indeed to supply

clean electrical power to systems, the power supply also interacts with themotherboard to perform an increasing number of functions, including CPU startup,system power down, voltage and temperature detection and other functions.

Power Good Signal:The signal is actually a logic level signal designed as a power supply

output signal to the CPU circuitry, to start the CPU running.

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Power On:Prior to the ATX standard, AT compatible power supplies either had the

power switch mounted on the back or side of power supply itself ,or had a remote

switch mounted on the front panel.The power on signal wire is apart of ATX standard and carries only a lowvoltage logic level signal from the motherboard to the power supply, telling itwhen to turn on and when to turn off.

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PRACTICAL NO 3

Aim:To make comparative study of mother boards: 386, 486, Pentium-I ,Pentium-II, Pentium-III.

Theory:

PENTIUM 1

Pentium (3.1M transistors in 273 pin pkg.)

Super scalar: multiple execution units, each pipelined with multiple stagesas opposed to Super pipeline (single execution unit with several pipeline stages)

Super scalar arch with 3 exec units: 2 for Integer data (5 stages ea), 1 forFPU (8 stages)

64 bit (8B) data bus.

Internal register size same as 386 and 486 ie 32 bit

32 bit adders bus (A31-A3)

8 BE (byte enable) pins (BE0, .., BE7) to access 8B data

8 DP (Data Parity) pins (DP0, .., DP7) pins to error-check 8B data 16KB on-chip cache: 8KB for code, 8KB for data

Cache org: 2-way set assoc, 8KB=128 sets of 64B, ea set = 2 lines, ealine=32B

Code cache is R-only

Data cache is R/W; uses write-though or write-back

Replacement policy for both caches is LRU

Branch prediction predicts a branch and loads it into pipeline units ahead oftime.

Pentium uses 4KB, and optional 4MB pages. 386/486 has 4KB for pagesize.

Uses 2 sets of TLBs: one for code & one for data. Data TLB has 64 entriesfor 4KB pages & 8 entries for 4M pages. Code TLB has 32 entries for 4KB pages& 32 entries for 4M pages 386/486 has 32 TLB entries.

Pentium has both bursts read and burst write.

PENTIUM 21

Is in same family (P6) as Pentium Pro except it incorporates MMX

Dual Independent Bus Arch. (dedicated 64B cache bus) 32K (16K+16K ) L1 cache 512K L2 cache

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Up to 4GB of addressable memory space.

Ease of Multiprocessing same as in Pentium Pro.

Feature 8086/88 286 386 486

# Addr. lines 20b (1MBAddr. Space

24b (16MBAddr. space

32b (4GB Addr.space)

32b (4GBAddr. space)

# Data lines 16b/8b 16 32b 32b

Register Sizes 16/8 16/8 32 32b

# clks per bus

cycle

4 2 2 1 viapipelining

Multiplexed

Addr/Data?

Yes No No

Protected

Mode?

No Yes. Protected toreal moderequires

hardwareresetting

Yes. Protected toreal mode switch by

software

Yes.Protected toreal modeswitch bysoftware

Virtual

Memory?

Yes withsegmentation

Yes: RealMode=1MB,

protected mode= 16MB

Yes Yes

Paging/

segmenting?

Segmentation

only

Seg Only Yes Yes

Cache?

No No Yes. External Cache.Address Cache (TLB)on-chip. TLB with 32

entries.

8KB on-chipcache for data+ instructions;

2-way setassoc. with

write-throughupdate

Virtual AddressSpace

14b seg. Regsallow addr

space of 214 .232 = 246 B = 64

TeraBytes

14b seg. Regsallow addr space

of 214 . 232 = 246 B= 64 TeraBytes

Parity Pins?

No No No Yes. 4 pinsone for each

data byte:DP0, , DP3

Math

Coprocessor?

No No Yes. Separate 387chip

Yes. On-chip

Extra Pins

2 pins: BRDY

(Burst RDY toMPU and

BLAST (Burst

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Last fromMPU)

Virtual 8086

Mode?

Default Yes Yes

ISSUE PENTIUM PENTIUM PRO (P6 code

name)

Year Introduced 1993 1995

# transistors 3.3X 106 5.5X106

#pins 273 387

Ext data bus 64 64

Address bus 32 36Phys Memory (MAX) 4GB 64GB

Virtual Memory 64TB 64TB

Data types (Reg size) 8, 16, 32 8, 16, 32

Cache1 (L1) 16KB (8K code, 8K data) 16KB (8K code, 8K data)

Cache2 (L2) External On same pkg, but differentdie (256KB/512KB)

Superscalar 2-way 3-way

#exec units 3 5

Super pipeline?

No (5 stages) Yes (12 stages. Due to

instructions being brokeninto RISC-like pieces calledmicro Ops.

Branch Prediction Yes Yes

Out-of-Order Exec

No Yes. With results stored intemporary regs. They arereleased as needed. Can go20-30 instructions deep.Retire Unit provides resultsin programmer visible regs

(eg. EAX, EBX,)Ease of Multiprocessing No yes

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PRACTICAL NO 4

Aim: Study the various cables, connections and parts used in computer

communication.

Theory:

Male vs. Female Connector: Im not going too far into this, but a maleconnector is the side of a connection that has the prongs--like the power plug onyour computer monitor. The side that goes from your monitor into the wall is themale. The outlet is the female side of the connector.

DB: This term you will see in the context of DB-25 or DB-9. What this isdescribing is the shape of the connector. The connector has a definite shape like acapital D (also could be called a trapezoid with rounded angles).

Now let's take a look at some of the various cable types.

Serial PortStandard : RS-232

Connector Name : DB-9 (most common) sometimes DB-

25Transfer mode : Asynchronous

Sometimes called : COM portsNumber found on a system : 2 possible of 4IRQ : 3(Com 1&3) and 4(Com 2&4)I/O range : COM 1=03f8-03ff COM 2=02f8-02ff

COM 3=3E8-3EF and COM

Max length : 50 feet

Max data rate : 1.5 Mbps (with 16550A UART)

Normally used with : This is normally seen on older mice andmodems. Two computers can benetworked together using a null modemcable. This is a serial cable that has itssend and receive crossed over so the 2computers are not trying to sendinformation to the other's send port.

Parallel Port

Standard : IEEE-1284Connector Name : DB-25(on PC), Centronics

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Transfer mode : SynchronousSometimes called : LPTNumber found on a system : 1 (up to 2)Max length : 10 Meters (approx. 30 feet) absolute

MaximumMax data rate : 4 Mbps

Normally seen on : You usually see this on printers andscanners. This is being replaced with

USB.

DIN 6Connector Name : DIN 6 (6 pin)

Sometimes called : PS/2 port, Mouse port, keyboard port,mini DIN 6Number found on a system : 2

DIN 5Connector Name : DIN 5Transfer mode : N/ASometimes called : old keyboard connectorNumber found on a system : 1IRQ : 1

USB 1.1

Standard : USB 1.1 (by USB-IF)ConnectorName : USB A/B

Transfermode : AsynchronousNumberfoundonasystem : 2-5Maximum number of Devices : 127IRQ : 11Maxlength : 3-5 metersMaxdatarate : 12 Mbit/sec (1.5 MB/sec)

Power : 2.5w

Features: To connect many devices, you can use a USB hub. This is a boxthat you connect into your computer through one of your USB ports andthen you can plug many other devices into it. Also, the speed of each USBchain is shared between all devices on that chain. So the more devices youhave operating at once, the slower they all will go.

USB 2

Standard : USB 2 (by USB-IF)Connector Name : USB

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Transfer mode : AsynchronousSometimes called : USB 2Number found on a system : Still being determinedIRQ : 11

Power : 2.5w

Firewire (IEEE-1394)

Standard : IEEE-1394

Connector Name : IEEE-1394 A BTransfer mode : Asynchronous/Isosynchronous

Sometimes called : Firewire, IEEE-1394 or iLink (Applecomputers has trademarked the termFirewire. So, if you see it called that,

someone is paying for that ability. iLinkis what Sony calls IEEE-1394).

Number found on a system : 2Max length : 4.5m (between devices)Max data rate : 100Mbps, 200Mbps, 400Mbps

(12.5MB/sec 255MB/sec 500MB/sec).Most computers support 400Mbps but

most devices are only 200MbpsMax # of devices : 63

Features: Some on the added features are that you do not need a PC toconnect them together. You could conceivably have a video cameraconnected to a DVD-R and burn your movies without needing a computerconnected to it. They can talk to one another without using up the bandwithto the computer and back. You can daisy chain them together so there is noneed for a hub as in USB. Also there is more power supplied. So, forexample, you have enough to have a hard disk drive running without powercoming from the wall. Some companies have set it up so you can connect

an MP3 player to your computer using IEEE-1394 and transfer the data plusrecharge the player's internal batteries off the firewire cable.

VideoIn this section we are not so worried about things like transfer rates

and IRQs. The monitor will only refresh so fast and IRQs would affect yourvideo board not your monitor. The point of this part is so that you canintelligently find and talk about these.

Standard : VGA (Video Graphics Array)

Connector Name : DB-15

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Quick recognition on a computer:This is our old standby and by far the most common of our video

connectors. It is easy to find. It is the only small three-rowed DB connector wewill find on a PC. It is usually away from the other connectors because it is on areplaceable card. There are, however, motherboards that do have video built in. Ifso, then this connector will be close to the other connectors.

Power

The power connector is almost completely standard. This looks almostexactly like an extension cord with the exception of the ground being a slotinstead of a round hole. Not much more to say. Make sure that the powerswitch on the back of your computer is set for the correct voltage (115 or230) for your location. Be careful with laptops and some newer AppleMacintosh computers that may have different looking power connectors on

the computer.

Minijack

Connector Name : 1/8 minijackSometimes called : headphone jackNumber found on a system : 1-5Telephone cable : RJ-11 is a common telephone cable.The end is called an RJ-11 connector and the

cable is called category 1 (Cat 1).

Ethernet cable

Standard : Conectors EIA/TIA 568a/b CablesCategory 3, 4, 5 or 5e

Connector Name : RJ-45Transfer mode : SerialSometimes called : Unshielded twisted pair (UTP) Shielded

twisted pair (STP just UTP with some

more shielding), 10BaseT, 100BaseT,1000BaseT.Crossover cable

Number found on a system : 1 (sometimes more)IRQ : Would be assigned to the Network

interface card.Max length : 100 meters (328 ft.)Min length : 1 Meter (3 ft.)Max data rate : 10/100/1000 Mbp/sec

There is also a Plenum-grade Ethernet cable. This is a cable that isnecessary for fire code. The issue is that if there is a fire and the PVC outercoating of non-Plenum grade cable catches on fire, it will release deadlygasses. In that case, if you have an enterprise grade network where you

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have literally thousands of these cables running through the walls, this cancause deadly results in a fire. Before wiring a building, check with the FireMarshall about needing this cable.

SCSI

Connector Name : DB25, IDC50, Centronics 50, HDI30,DB50, HPDB50, HPDB68, HP

Centronics 60, HP Centronics 68, SCA 80-Pin, and VHDCI68Number found on a system : SCSI devices can be daisy chained, sothe number connected to a system will vary

Max length : 1.5 meters to 25 meters depending onthe typeMax data rate : 360 MB/sec max50 Pin Centronics : This is connector is at the device end of

some peripherals

25 Pin D Sub:This one you have to look out for. You can plug a parallel connector into

this and they will match up perfectly. But this is found on an AppleMacintosh. To help you out, you will not find a parallel connector on a Macmaking this easy. If you are working on a Mac, it is a SCSI interface not aparallel connector.

DB-50:

This is a rare connector that has 3 rows of pins. It was used on HP and DECcomputers. It is not very common.

50 Pin MicroD (High Density): This is a connector that has 2 rows ofsquared off holes. It is used on 8-bit fast SCSI.

68 Pin MicroD: This looks like the 50 Pin MicroD but longer and withmore pins. This interface is used on all SCSI Wide connectors.

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PRACTICAL NO 5

AIM: To study various cards used in a system.

DISPLAY CARD :-

Three components in a video card

The video card is just as important as the screen and more often overlooked.During the years 1999-2001 the overall quality of video adapters has beenimproved. Earlier there were some very lousy products in the market. Follow myarticles to know more of the video adapter. A video card is typically an adapter, aremovable expansion card in the PC. Thus, it can be replaced. The video card canalso be an integral part of the system board this is the case in certain brands of PCsand is always the case in lap tops. I have a clear preference for a replaceable videocard in my stationary PC. However modern motherboard may include goodintegrated video chip sets. You just have to know which ones!

Regardless of whether it is replaceable or integrated, the video adapter consists ofthree components:

A video chip set of some brand (ATI, Matrox, Nvidia, S3, Intel, toname some of the better known). The video chip creates the signals,which the screen must receive to form an image.

Some kind ofRAM (EDO, SGRAM, or VRAM, which are all variationsof the regular RAM). Memory is necessary, since the video card must beable to remember a complete screen image at any time. Using AGP, thevideo card may use the main memory of the motherboard.

A RAMDAC - a chip converting digital/analog signals. Using Flatpanel monitors, you do not need a the function of a RAMDAC.

Video cards always have a certain amount of RAM. This RAM is alsocalled the frame buffer. Today video cards hold plenty of RAM, butbefore it was more important:

How much RAM? That is significant for color depth at the highestresolutions.

Which type RAM? This is significant forcard speed.

Video card RAM is necessary to keep the entire screen image inmemory. The CPU sends its data to the video card. The video processorforms a picture of the screen image and stores it in the frame buffer.

This picture is a large bit map. It is used to continually update the screenimage.

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e Amount of RAMOlder video cards were typically available with 1, 2, 4 or more MB RAM. Howmuch is necessary? That depends primarily on how fine a resolution you want onyour screen. For ordinary 2D use, 16 bit colors are "good enough." Let us look at

RAM needs for different resolutions:

Note that the video RAM is not utilized 100% for the bit map. Therefore, 1 MB isnot enough to show a 800 x 600 picture with 16 bit colors, as the abovecalculation could lead you to believe. Today video cards come with 4 MB, 8 MBormore RAM.

Using ordinary RAM, you saw speed improvements of the graphics card using 4MB instead of2 MB, if the resolution only was 800 x 600 or 1024 x 768. In thiscase data can be written to and read from the RAM simultaneously - usingdifferent RAM cells. With only 2 MB RAM, data sometime had to wait for a freecell.

SOUND CARDS:-Sound cards have a minimum of four tasks. They function as:

The synthesizer

The synthesizer delivers the sound. That is, the sound card generates the sounds.Here we have three systems:

FM synthesis, Frequency Modulation Wave table

Physical modeling

The A/D conversion:

You need a A/D conversion, when analog sound signals are recorded, i.e. from amicrophone. The other way around, the D/A-converter is used when the digitalsounds have to be reproduced into a signal for the speakers amplifier.The acousticwaves are collected by the microphone and lead to the sound card. Here it is

converted into series of digital pulses, which eventually are saved in a file. Thisway a sampling is an analog-to-digital conversion:

Sampling

As mentioned is the basic concept of digital recording of sound is called sampling.You can record any sound you want into a sample (a Wav file) if you have a soundcard and a microphone. The sampling can be done in various qualities:

8 bit or 16 bit sampling

11, 22 or 44 KHz (kilohertz)

Stereo or mono

The number of kilohertz tells how many thousand times per second the sound willbe recorded.

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LAN CARDS :-

LAN card is used in networking. It accepts the analog signal from one pc andtransfers it to another through a cable. This cable is generally twisted pair orcategory 5.

LAN card works on the voltage of+12 volts it mount in the two slots, in the latestconfiguration these are mounted in the PCI slots, on the receiving end it receivethe data in the analog form and convert it into the equivalent digital form whichwill be stored in the buffer of the system. The connector of the cable generally inround shape female connector the data transfer speed of the LAN card generallyvary according to the models. The clock used by the LAN card control on its ownlevel.

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PRACTICAL NO 6

AIM: To remove, study and replace floppy disk drive.

Theory:

The floppy disk drive (FDD) was the primary means of adding data to a computer

until the CD-ROM drive became popular. In fact, FDDs have been a keycomponent of most personal computers for more than 20 years. Basically, a floppydisk drive reads and writes data to a small, circular piece of metal-coated plasticsimilar to audio cassette tape.

Very few PC's are without a floppy drive. Diskettes were developed as a low costalternative to hard disks. In the 60's and 70's, when hard disk prices wereexorbitant, it was unthinkable to use them in anything but mainframe and minicomputers. The first diskettes were introduced in 1971. They were 8" diameterplastic disks with a magnetic coating, enclosed in a cardboard case. They had a

capacity of one megabyte. The diskettes are placed in a drive, which has read andwrite heads. Conversely to hard disks, the heads actually touch the disk, like in acassette or video player. This wears the media.Later, in 1976, 5.25" diskettes were introduced. They had far less capacity (only160 KB to begin with). However, they were inexpensive and easy to work with.For many years, they were the standard in PC's. Like the 8" diskettes, the 5.25"were soft and flexible. Therefore, they were named floppy disks.

In 1987 IBM's revolutionary PS/2 PC's were introduced and with them the 3"hard diskettes we know today. These diskettes have a thinner magnetic coating,

allowing more tracks on a smaller surface. The track density is measured in TPI(tracks per inch). The TPI has been increased from 48 to 96 and now 135 in the3.5" diskettes.Here we see the standard PC diskette configurations:

Diskette size Name Tracks perside

Number of sectorsper tracks

Capacity

5.25" Singleside

SD8 40 8 40 X 8 X 512 bytes = 160KB

5.25" Double DD9 40 9 2 X 40 X 9 X 512 bytes =

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side 360 KB

5.25" Doubleside

High Density

DQ15 80 15 2 X 80 X 15 X 512 bytes =1.2 MB

3.5" DD DQ9 80 9 2 X 80 X 9 X 512 bytes =720 KB

3.5" HD DQ18 80 18 2 X 80 X 18 X 512 bytes =1.44 MB

3.5" XD( IBM only)

DG36 80 36 2 X 80 X 36 X 512 bytes =2.88 MB

Diskette drives turn at 300 RPM. That results in an average search time (revolutions) of 100 ms.

The floppy controller

All diskette drives are governed by a controller. The original PC controller wasnamed NEC PD765. Today, it is included in the chip set, but functions like a 765.It is a programmable chip. It can be programmed to handle all the various floppydrive types: 5.25" or 3.5" drives, DD or HD etc.

The controller has to be programmed at each start up. It must be told which drivesto control. This programming is performed by the start up programs in ROM (readmodule 2a). So you don't have to identify available drive types at each start up,these drive parameters are saved in CMOS RAM. The floppy controller reads datafrom the diskette media in serial mode (one bit at a time like from hard disks).Data are delivered in parallel mode (16 bits at a time) to RAM via a DMA channel.Thus, the drives should be able to operate without CPU supervision. However, inreality this does not always work. Data transfer from a diskette drive can delay andsometimes freeze the whole PC, so no other operations can be performed

simultaneously.

Parts of a Floppy Disk Drive:

The Disk

1. A floppy disk is a thin plastic base material coated with iron oxide. This oxide isa

ferromagnetic material, meaning that if it is exposed to a magnetic field it ispermanently magnetized by the field.

2. It can record information instantly.3. It can be erased and reused many times.4. These are very inexpensive and easy to use.

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The Drive:- The major parts of a FDD include:

Read/Write Heads: Located on both sides of a diskette, they move together on

the same assembly. The heads are not directly opposite each other in an effort toprevent interaction between write operations on each of the two media surfaces.The same head is used for reading and writing, while a second, wider head is usedfor erasing a track just prior to it being written. This allows the data to be writtenon a wider "clean slate," without interfering with the analog data on an adjacenttrack.

Drive Motor: A very small spindle motor engages the metal hub at the center ofthe diskette, spinning it at either 300 or 360 rotations per minute (RPM).

Stepper Motor: This motor makes a precise number of stepped revolutions tomove the read/write head assembly to the proper track position. The read/writehead assembly is fastened to the stepper motor shaft.

Mechanical Frame: A system of levers that opens the little protective window onthe diskette to allow the read/write heads to touch the dual-sided diskette media.An external button allows the diskette to be ejected, at which point the spring-loaded protective window on the diskette closes.

Circuit Board: Contains all of the electronics to handle the data read from orwritten to the diskette. It also controls the stepper-motor control circuits used tomove the read/write heads to each track, as well as the movement of the read/writeheads toward the diskette surface.

Tools You May Need :

Depending on the design of you computer, you may need the following tools tocomplete the installation

A Flat blade screwdriver A Phillips screwdriver

Needle-nosed pliers

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Handling the 1.44 Floppy Drive :

Your 1.44 drive must be handled with care. Avoid applying undue force orabnormal strain to the spindle motor, stepping motor or printed circuit board.Avoid placing your fingers on the printed circuit board. It is best to hold the 1.44drive by the diecast frame, as indicated by the arrows in Figure A. Never loosen

the fixing screw of the printed circuit board, etc.

Applications:Floppy disks, while rarely used to distribute software (as in the past), are still usedin these applications:

1. For software recovery after a system crash or a virus attack2. When data from one computer is needed on a second computer and the twocomputers are not networked.3. In bootable diskettes used for updating the BIOS on a personal computer

4. In high-density form, used in the popular Zip drive.

Procedure:

1. Switch off the main power supply.

2. Take out the data bus & the power supply from the FDD, gently.

3. Unscrew the FDD & take it out with extreme care.

4. Now put the FDD back in & screw up.5. Plug in the data bus & power supply & make sure that the connections are

precise.

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PRACTICAL NO 7

AIM: To remove, study and replace Hard disk drive.

Theory:Hard disks were invented in the 1950s. Hard disks have a hard platter that holdsthe magnetic medium, as opposed to the flexible plastic film found in tapes andfloppies. At the simplest level, a hard disk is not that different from a cassette tape.Both hard disks and cassette tapes use the same magnetic recording techniques.Hard disks and cassette tapes also share the major benefits of magnetic storage --the magnetic medium can be easily erased and rewritten, and it will "remember"the magnetic flux patterns stored onto the medium for many years.

A modern hard disk is able to store an amazing amount of information in a smallspace. A hard disk can also access any of its information in a fraction of a second.A typical desktop machine will have a hard disk with a capacity of between 10 and40 gigabytes. Data is stored onto the disk in the form of files. A file is simply anamed collection of bytes. The bytes might be the ASCII codes for the charactersof a text file, or they could be the instructions of a software application for thecomputer to execute, or they could be the records of a data base, or they could bethe pixel colors for a GIF image. No matter what it contains, however, a file issimply a string of bytes. When a program running on the computer requests a file,

the hard disk retrieves its bytes and sends them to the CPU one at a time.

There are two ways to measure the performance of a hard disk:

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Data rate - The data rate is the number of bytes per second that the drivecan deliver to the CPU. Rates between 5 and 40 megabytes per second arecommon.

Seek time - The seek time is the amount of time between when the CPUrequests a file and when the first byte of the file is sent to the CPU. Timesbetween 10 and 20 milliseconds are common.

The platters typically spin at 3600 or 7200 rpm when the drive is operating. Theseplatters are manufactured to amazing tolerances and are mirror-smooth. In order toincrease the amount of information the drive can store, most hard disks havemultiple platters.

Annotated illustration of a typical PC actuator assembly, showing the majorcomponents. The platters have been removed from the drive to provide a betterview of the actuator arms and heads. There are four sliders but only

one of each pair is visible. The spindle motor is visible at the top right.

The arm that holds the read/write heads is controlled by the mechanism in theupper-left corner, and is able to move the heads from the hub to the edge of thedrive. The arm and its movement mechanism are extremely light and fast. The armon a typical hard-disk drive can move from hub to edge and back up to 50 timesper second.

Data is stored on the surface of a platter in sectors and tracks. Tracks are

concentric circles, and sectors are pie-shaped wedges on a track. A sector containsa fixed number of bytes -- for example, 256 or 512. Either at the drive or theoperating system level, sectors are often grouped together into clusters.The process of low-level formatting a drive establishes the tracks and sectors onthe platter. The starting and ending points of each sector are written onto theplatter. This process prepares the drive to hold blocks of bytes. High-levelformatting then writes the file-storage structures, like the file-allocation table, intothe sectors. This process prepares the drive to hold files.

The data bus connecting hard disk to the motherboard is of 32 bits & 39 pins. The

power supply from the SMPS is a 4 pin supply that goes into the hard disk. Jumpersettings for the various configurations of the hard disk are shown below:

Jumper settingIDE/ATA hard disks are fairly standard in terms of jumpers. There are usuallyonly a few and they don't vary greatly from drive to drive. Here are the jumpersyou will normally find:

Drive Select: Since there can be two drives (master and slave) on thesame IDE channel, a jumpers is normally used to tell each drive if it shouldfunction as a master or slave on the IDE channel. For a single drive on a

channel, most manufacturers instruct that the drive be jumpered as master,while some manufacturers (notably Western Digital) have a separate settingfor a single drive as opposed to a master on a channel with a slave. The

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terms "master" and "slave" are misleading since the drives really have nooperational relationship.

Slave Present: Some drives have an additional jumper that is used totell a drive configured as master that there is also a slave drive on the ATAchannel. This is only required for some older drives that don't supportstandard master/slave IDE channel signaling.

Cable Select: Some configurations use a special cable to determinewhich drive is master and which is slave, and when this system is used acable select jumper is normally enabled.

Size Restriction Jumper: Some larger hard disk drives don't workproperly in older PCs that don't have a BIOS program modern enough torecognize them. To get around this, some drives have special jumpers that,when set, will cause them to appear as a smaller size than they really are tothe BIOS, for compatibility. For example, some 2.5 GB hard disks have ajumper that will cause them to appear as a 2.1 GB hard disk to a system that

won't support anything over 2.1 GB. These are also sometimes calledcapacity limitation jumpers and vary from manufacturer to manufacturer.

The most common interface for PC hard disks is called IDE, which in fact standsfor Integrated Drive Electronics. This name is something of a misnomer today.When it was introduced, IDE was distinguished from the other interfaces of theday by having the integrated electronics on the drive, instead of on the controllercard plugged into the system bus like older interfaces. However, the term reallyrefers to where the control logic is and not the interface itself, and since all harddisks today use integrated electronics the name doesn't mean anything any more,

despite the fact that everyone continues to use it. The other popular PC hard diskinterface today, SCSI, also uses drives that have integrated controllers. The morecorrect name for the IDE interface is AT Attachmentor ATA.

Spindle speeds

SpindleSpeed (RPM)

AverageLatency (HalfRotation) (ms)

Typical Current Applications

3,600 8.3 Former standard, nowobsolete

4,200 7.1 Laptops

4,500 6.7 IBM Microdrive, laptops

4,900 6.1 Laptops

5,200 5.8 Obsolete

5,400 5.6 Low-end IDE/ATA, laptops

7,200 4.2High-end IDE/ATA, Low-endSCSI

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10,000 3.0 High-end SCSI

12,000 2.5 High-end SCSI

15,000 2.0 Top-of-the-line SCSI

Procedure:1. Switch off the main power supply.2. Take out the data bus & the power supply from the hard disk, gently.3. Unscrew the hard disk & take it out with extreme care.4. Now put the hard disk back in & screw up.5. Plug in the data bus & power supply & make sure that the connections are

precise.

Fitting the Hard Disk Drive

Unpack the HDD. Make sure at this stage that you have your anti-static measuresin place, and even briefly make contact with both hands on the metal of the case tomake sure.Locate the IDE Configuration Pins on the HDD. These can usually be found nextto the power and data connections, and will be a group of six or eight small pinswith a small plastic 'jumper' attached between two of the pins. If this is to be theonly HDD in your PC, then set this to Master. Alternatively, if this is to be anadditional HDD then it must be set to Slave.The Hard Drive differs from the Floppy Drive in that it is usually inserted from

within the PC case. On one end of the Hard Drive will be the sockets forconnecting the cables. This end must point into the case such that the cables can beconnected later on. Gently slide the Hard Drive into the bay that now holds thefloppy drive above. Move the drive around until you find the fixing points and usethe standard screws to secure it. Clear any obstructions to this insertion from insidethe case if necessary.

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PRACTICAL NO 8

AIM: To remove, study and replace CD ROM drive.

Theory:

The Optic Medias (CD ROM's and DVD)

CD ROM and DVD are optic readable media, contrary to hard disks, floppy disksand tapes, which are magnetic. The optic storage media are read with a very thin

and very precisely aimed laser beam. They supplement the magnetic media. Theyhave clear advantages in the areas of data density and stability: Data can be packedmuch more densely in an optic media than in a magnetic media. And they havemuch longer life span. It is presumed that a magnetic media, such as a hard disk orDAT (digital audio tape) can maintain their data for a maximum of five years. Themagnetism simply fades away in time. Conversely, the life span of optic media iscounted in tens of years.

The Compact DiskThe compact disk (CD) was introduced by Philips and Sony in 1980 to replace LP

records. It is a small plastic disk with a reflecting metal coating, usually aluminum.Myriad's of tiny indentations are burned into this coating. These indentationscontain the music in millions ofbits. The CD is organized in tracks. Each track isassigned a number.The big advantage of the CD is its high-quality music reproduction and totalabsence of back ground noise as well as a great dynamic. During operation, thesoftware in the drive can correct errors caused by such things as finger marks onthe disk. All in all, the CD is an excellent music storage media.

The CD-ROM

The CD-ROM (Read Only Memory) came as an extension of the CD in 1984. Inprinciple, the media and the drives are the same. The difference is in the datastorage organization. In a CD-ROM, the data are stored in sectors, which can beread independently -Like from a hard disk.The CD-ROM has become an important media in the PC world. It can hold 650MB of data, and it is very inexpensive to produce. Today, there are three types ofCD drives and DVD drives are on their way:

Drive Type Name The Drive Can

CD- ROM Compact Disk Read Only Read CD-ROM and CD-

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Memory R

CD-ROM Multithread --/-- Read CD-ROM, CD-R And CD-E

CD-R Compact Disk Recordable Read CD-ROM and CD-R. Write once on special

disks named CD-RCD-E or CD-RW Compact Disk Erasable orCompact Disk Rewritable

Read CD-ROM and CD-R. Write once on specialdisks named CD-E

DVD RAM Digital Versatile Disk Random Access Memory

Reads all CD formats.Read DVD ROM. Readand write DVD disks

Let us start by look at the CD-ROM construction. To facilitate understanding, it

will be easiest to compare it with other disk types, especially the hard disk. TheCD-ROM is a plastic disk of 4.6" diameter. It is placed in a CD-ROM drive, whichis like a drawer in the PC cabinet :

When the CD-ROM disk is placed in the drive, it starts to spin the disk. It reachesoperating speed in one to two seconds. Then the drive is ready to read from thedisk.

About Optic Data StorageThe CD-ROM can be compared to a floppy drive, because the disks areremovable. It can also be compared with a hard drive, because of similar datastorage capacity. Actually, a CD-ROM disk can hold up to 680 MB of data. This

equals the capacity of 470 floppy disks. However, the CD ROM is neither a floppynor a hard disk! While floppy and hard disks are magnetic media, the CD-ROM isan optic media. The magnetic media work in principle like an audio cassette tapeplayer. They have a read/write head, which reads or writes magnetic impressionson the disk. The magnetic media contains myriads of microscopic magnets, whichcan be polarized to represent a zero or numeral one (one bit).In the optic readable CD-ROM, the data storage consists of millions ofindentations burnt into the lacquer-coated, light-reflecting silver surface. The burntdents reflect less light than the shiny surface. A weak laser beam is sent to the diskthrough a two-way mirror and the sensor registers the difference in light reflection

from the burnt and shiny areas as zero's and one's.

Rotation speed and data transmission

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There are different generations of CD-ROM drives. Here you see their data.

CD-ROM Type Data Transfer Speed RPM Outmost-innermost Track

1X 150kb/sec 200-530

2X 300 kb/sec 400-10604X 600 kb/sec 800-2120

8X 1.2MB/Sec 1600-4240

12X-24X 1.8 3.6 MB/Sec 2400-6360

The new drives are 24X and 32X spin. When you see their rotation speeds, youwonder how much further this technology can be advanced. The hard disk can spinat high speeds, because it operates in sealed box. The CD does not.

Procedure:1. Switch off the main power supply.2. Take out the data bus & the power supply from the drive, gently.3. Unscrew the CD ROM & take it out with extreme care.4. Now put it back in the cabinet from the front & screw up.5. Plug in the data bus & power supply & make sure that the connections are

precise.

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PRACTICAL NO 9

AIM: To study the monitor, its circuitry and various presets and some

elementary fault detection.

MONITOR ABCsThe monitor is a hardware device which physically connects to your CPU. The

monitor allows information and current status be be visually outputted similar to aTV. Like most TVs the computer monitor has a CRT or Cathode Ray Tube whichfound inside the computer monitor as illustrated in the above picture. The CRT isthe main component and most expensive part within your computer monitor.Within the CRT are three electron guns, Red, Green and Blue. Each of these gunsstreams a steady flow of electrons left to right for each line of your monitor. As theelectrons hit the phosphors on the CRT the phosphor will glow certain intensities.As a new line begins the guns will then begin at the left and continue right, theseguns will repeat this process sometimes thousands of time until the screen has beencompletely drawn line by line. Once the phosphors on the CRT have been hit with

an electron they will only glow for a short period of time, because of this the CRTmust be refreshed which means the process will be repeated as explained above. Ifthe video cards refresh rate is not set high enough you may encounter a flicker or anoticeable steady line scrolling from the top to the bottom of your screen. If youare encountering this issue, resolutions have been described on our video cardpage.

DOT PITCH

The dot pitch is a measurement; measured in millimeters which is the amount ofspace between the phosphors on a computer monitor screen. The smaller thenumber of dot pitches the sharper the image.

GHOST / BURN

If monitors especially older CGA / EGA monitors are left on for long duration's oftime as the electron beams cause the phosphors to glow. If the electron gunscontinue to do this for thousands of hours refreshing the same images this cancause the images to be burnt into the CRT surface causing a ghost image to appear.

This image will become permanently displayed on your monitor for the durationof its life.A resolution to this problem is screen savers, which is a program whichgenerates a random set of images, lines or other methods of allowing the image to

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not remain static while the computer is not being used.While new monitors (VGA /SVGA) do not have this issue screen savers are still commonly used today, youcan find screen savers in our screen saver download section.

MONITOR CONTROLS

The following is additional information on the likely monitor controls on yourmonitor. Using these controls you can help improve the quality and layout of thepicture on your monitor for better viewing pleasure. Please keep in mind that notall

Monitors will have all of the available buttons.

Power - Turns the monitor on / off.Brightness - Using this button or wheel the user can increase and decrease thebrightness on the screen.

Contrast - Using this button or wheel can increase and decrease the amount ofcontrast on the screen.Horizontal Size - Allows for the picture on the screen to be stretched to thehorizontal edge of the monitor.Vertical Size - Allows the picture on the screen to be stretched to the verticaledges of the monitor.

Horizontal Position - Allows the picture to move moved horizontally, once in thecenter the user can then use the Horizontal size to stretch it to have an equalamount of black border on each side.Vertical Position - Like the Horizontal Position, using this button or wheel theuser can move the picture up or down to center the picture more appropriately.Full Screen - Sets monitor to full screen

Degauss - This button will demagnetize the CRT restoring possible colorimpurities. After this button has been pressed the degaussing circuit will beactivated and then deactivated after a few seconds. Pressing and holding thisbutton for a few seconds may cause your computer monitor to reset all data.

Corner / Trapezoid Correction - Using this button or wheel the user can eitherround the edges of the picture or move the picture inward like an hour glass oroutwards.Vertical Linearity - Sets the width of the vertical lines.Moir - Removes or reduces the effect if any.OSD Controls - If the monitor contains OSD controls allows for the OSD menusto be adjusted.Power Management - Allows the user to define the power management settingsthrough the monitor itself and not the software.Monitor Status - Displays the current monitor settings such as refresh rate andother settings.Language - Sets the language on the monitor.

MINIMUM RESOLUTION

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The size is an important factor of the computers running resolution. When pickingthe resolution try basing it off the monitors size for best use.

13-inch 640 x 480

15-inch 800 x 60017-inch 1,024 x 76821-inch 1,280 x 1,024

Resolution Bit map size with 16 bit colors Necessary RAM on the video card

640 x 480 614,400 bytes 1 MB

800 x 600 960,000 bytes 1.5 MB

1024 x 768 1,572,864 bytes 2 MB1152 x 864 1,990,656 bytes 2.5 MB

1280 x 1024 2,621,440 bytes 3 MB

1600 x 1200 3,840,000 bytes 4 MB

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PRACTICAL NO 10

AIM: To study printer assembly and elementary fault detection of LASER

and DMP.

How Laser Printer Works

Copiers and laser printers have a lot in common. The major difference is in howthe image is formed on a photosensitive drum:

A copier uses a bright light and lens to focus an image of the original(actually, a strip at a time which is scanned in most modern low to mediumperformance copiers) onto the drum. Adjusting the lens-to-original andlens-to-drum distance is used to vary the reduction or magnification.

A laser printer uses a low power sharply focused laser beam to scanone line at a time on the drum. Modern laser printers use infra-red solidstate laser diodes similar to those used in CD players and optical disk driveswhile older ones used helium neon lasers.

LED printers use a large array of LEDs as the image source but are

otherwise similar to laser printers.

Beyond this, copiers and laser printers are nearly identical (at least in principle)except that copiers use a positive process (dark areas in the original result in markson the paper) and laser printers commonly use a negative process (a spot of lightresults in a dark mark on the paper).

All of the following takes place as a continuous process as the drum rotates.Note that the actual photosensitive drum in most copiers and laser printers has acircumference that is much smaller than the length of the printed page. Therefore,

only a portion fits at any given time and the charging, exposure, transfer to thepaper, cleaning, and erasing is a continuous process: The drum's surface is chargedto a high positive voltage (typically 5 to 6 kV) by a set of charging corona wires inclose proximity to the drum.

The exposure process differs for copiers and laser printers:

For laser printers, the negative image of the page stored in theprinter's buffer memory (the laser is turned on where the print is to beblack) is read out and scanned onto the drum one line (i.e., 1/300th or1/600th of an inch) at a time.

Where the light hits the drum's surface, its resistance drops dramatically and thecharge in these areas is dissipated.

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into a single powder), developer magnet (really neat!), cleaning blades, some ofthe corona wires.

How Dot Matrix Printers Works

Ever since the Digital era started, the Dot Matrix printing method is in vogue.Likeatom being the smallest indivisible entity in an element ,a dot in the dot matrixprinting is the smallest entity. In the digital era, the printing method evolvedaround 2 types-Impact and Non-Impact Printing.

In an Impact printing a mechanical force is exerted on the printing media to form acharacter whereas in the Non-impact printing the character formation on the mediais achieved through non-mechanical means like light(Laser), heat(Thermal),liquid(Inkjet)etc.

In Dot-Matrix printing, each character is divided into dots of rows and columnsand stored into computer memory. By suitably placing the dots, any character canbe formed. With this method just by changing the program, character shapes andsizes can be changed at will. This is a major advantage over the other method thathas made it so popular among the printing methods.

In multi-linguistic countries like us , the same printer can be used to print in anylanguage with only a program change. Dot-matrix printing method is used in bothImpact and Non-Impact form of printing. In the market worldwide popularlyknown as DMPs use Impact type of Dot-Matrix printing where as thermal printers,

Laser printers and Inkjet printers use Non-Impact type of Dot-Matrix printing.Even though all the above printers use dot matrix method, the acronym DMP isalways synonymous with Impact dot-matrix printer because of its popularity andolder technology. This means that nobody calls Laser or Inkjet printers as DMP'seven though they are DMP's.

Worldwide DMPs evolve around 9 pin and 24-pin printer heads to formcharacters .The pins are activated serially through a printer ribbon to formcharacter on the paper.

The Key specification and details of a typical DMP is as follows :

No of Pins

9 or 24. 9 pin is used for transactional/internal document printing whereQuality is not the key criteria. On the other hand, 24pin DMP offers better qualityprinting.

80col/136cl

Represents the paper size the printer can print -A4 size on 80col and A3

size on 136col.300cps speed

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Represents the printing speed of the DMP expressed in no of characters persecond. Normally speed in cps is mentioned against size of the character incharacter per inch, cpi.

Push/Pull tractor

How the continuous stationary is transported for printing in the DMP.Pushtractor is the normal one where in the tractor pushes the paper in to theprinter. In a Pull tractor printer, the tractor is situated after the print headand pulls the printer paper out of the printer. A convertible push-pull tractoris a tractor which can function both as push as well as pull tractor bychanging its position. Dual tractor printers are those which have twotractors. Dual tractors are usually found in multiple paper path printers, ie.front, top/rear & bottom paper paths.

Interface

Printer interfaces are Centronics parallel or RS232/422 serial or both. It isthe port through which PC and Printer are connected thru a cable. Someprinters are also have the option of USB interface.

AutoShare

Some printers with both serial & parallel interfaces can be connected to 2PCs simultaneously, one through parallel port and the other through serial port.The printer senses which PC is sending data and switches to the correspondingport. This feature is called AutoShare and is widely used to share 1 printer across2 PCs. AutoShare is a special feature and not all printers with both serial &

parallel port come with it.

Paper Path

There are various ways by which you can load/eject paper and park yourdifferent types of stationary on the printer for switching between them. Oneis friction mode for cut sheets, another is tractor more for continuous sheets.These can be from the rear, front, top or even bottom. More the no of paths,better is the flexibility of the printer's paper handling.

Language Printing capability

Normal DMP's understands only ASCII and indian language standard is in

ISCII.Any non ascii character is printer as graphics in DMP and due to thisthe speed of printing drops dramatically.In language DMP,the font of thelanguage is built in to the printer and hence even ISCII is printer incharacter mode and not in graphic mode.Language printers are eitherbilingual or multilingual.In bilingual DMP,one language other than englishcan be printed in text mode.In bilingual DMP,more than one language canbe printer in text mode along with english.

Key Application areas for DMP:

1. Bill,Invoice,PO printing2. Transactional document printing3. Label and Barcode printing

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4. Correspondence,Presentation and Report Printing5. Desktop publishing6. Utility bills printing -english and language

Advantages of a DMP over other Print technologies :

1. Lowest cost per page-less than 5 paisa/page2. Multi-part printing capability in one go-typically from 2 to 8 copies3. Lowest cost of ownership4. Rugged and reliable5. Acceptable print quality in text

Disadvantages of DMP over other Print technologies:

1. No multi color print capability

2. Poor print quality in graphics3. Noisy since it is impact printer compared to laser and inkjet4. Requires higher shelf space5. Slower print speeds in Letter quality printer.

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telephone industry. This standard designates which wire goes with each pin insidethe connector.

Categories of Unshielded Twisted Pair

Type Use

Category 1 Voice Only (Telephone Wire)

Category 2 Data to 4 Mbps (Local Talk)

Category 3 Data to 10 Mbps (Ethernet)

Category 4 Data to 20 Mbps (16 Mbps Token Ring)

Category 5 Data to 100 Mbps (Fast Ethernet)

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be susceptible to radio and electricalfrequency interference. Shielded twisted pair (STP) is suitable for environmentswith electrical interference; however, the extra shielding can make the cables quitebulky. Shielded twisted pair is often used on networks using Token Ring topology.

Coaxial Cable

Coaxial cabling has a single copper conductor at its center. A plastic layer providesinsulation between the center conductor and a braided metal shield (See fig. 3).The metal shield helps to block any outside interference from fluorescent lights,motors, and other computers.

Although coaxial cabling is difficult to install, it is highly resistant to signalinterference. In addition, it can support greater cable lengths between networkdevices than twisted pair cable. The two types of coaxial cabling are thick coaxialand thin coaxial.Thin coaxial cable is also referred to as thinnet. 10Base2 refers to

the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers tothe approximate maximum segment length being 200 meters. In actual fact themaximum segment length is 185 meters. Thin coaxial cable is popular in schoolnetworks, especially linear bus networks.Thick coaxial cable is also referred to asthicknet. 10Base5 refers to the specifications for thick coaxial cable carryingEthernet signals. The 5 refers to the maximum segment length being 500 meters.Thick coaxial cable has an extra protective plastic cover that helps keep moistureaway from the center conductor. This makes thick coaxial a great choice whenrunning longer lengths in a linear bus network. One disadvantage of thick coaxialis that it does not bend easily and is difficult to install.

Coaxial Cable Connectors

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The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are availablefor BNC connectors, including a T-connector, barrel connector, and terminator.Connectors on the cable are the weakest points in any network. To help avoidproblems with your network, always use the BNC connectors that crimp, ratherthan screw, onto the cable.

Fiber Optic Cablefiber optic cabling consists of a center glass core surrounded by several layers ofprotective materials (See fig. 5). It transmits light rather than electronic signalseliminating the problem of electrical interference. This makes it ideal for certainenvironments that contain a large amount of electrical interferenceFacts about fiberoptic cables:

Outer insulating jacket is made of Teflon or PVC.

Kevlar fiber helps to strengthen the cable and preventbreakage. A plastic coating is used to cushion the fiber center. Center (core) is made of glass or plastic fibers.

Fiber Optic Connector

The most common connector used with fiber optic cable is an ST connector. It isbarrel shaped, similar to a BNC connector. A newer connector, the SC, isbecoming more popular. It has a squared face and is easier to connect in a confined

space.

Installing Cable - Some Guidelines

When running cable, it is best to follow a few simple rules:

Always use more cable than you need. Leave plenty of slack. Test every part of a network as you install it. Even if it isbrand new, it may have problems that will be difficult to isolate later. Stay at least 3 feet away from fluorescent light boxes and

other sources of electrical interference. If it is necessary to run cable across the floor, cover the cablewith cable protectors. Label both ends of each cable. Use cable ties (not tape) to keep cables in the same locationtogether.

Network Communication devices

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A LAN comprises of different communication devices across the network such asthe following :

Repeater : A Device that amplifies and regenerates signals , so that theycan travel for longer distance on the cable.

Router : The basic function of the router is to route the traffic from onenetwork to another network efficiently. It provide intelligent redundancyand security required to select the optimum path. Usually routers are usedfor connecting remote networks.

Hub : A typical hub is a multi-port repeater. The signals received at thebackbone is regenerated and transmitted to all other ports.

Switch : This is a device with multiple ports which forwards packets fromone port to another. In case of 10Mbps Ethernet switch, each port supportsdedicated 10Mbps bandwidth. Ethernet switch is fast emerging as areplacement of the traditional thick backbone and best way to improveperformance of the network

Ethernet Cable Summary

Specification Cable Type Maximum length

10BaseT Unshielded Twisted Pair 100 meters

10Base2 Thin Coaxial 185 meters

10Base5 Thick Coaxial 500 meters

10BaseF Fiber Optic 2000 meters

100BaseT Unshielded Twisted Pair 100 meters

100BaseTX Unshielded Twisted Pair 220 meters

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PRACTICAL NO 12

AIM: To study parts of the keyboard and mouse.

The part of the computer that we come into most contact with is probablythe piece that we think about the least. But the keyboard is an amazing piece oftechnology. For instance, did you know that the keyboard on a typical computersystem is actually a computer itself? At its essence, a keyboard is a series ofswitches connected to a keyboard matrix that monitors the state of each switch andinitiates a specific response to a change in that state

Inside the Keyboard

The processor in a keyboard has to understand several things that are important tothe utility of the keyboard, such as:

Position of the key in the key matrix. The amount ofbounce and how to filter it.

The speed at which to transmit the typematics.

The key matrix is the grid of circuits underneath the keys. In all keyboards exceptfor capacitive ones, each circuit is broken at the point below a specific key.Pressing the key bridges the gap in the circuit, allowing a tiny amount of current toflow through. The processor monitors the key matrix for signs of continuity at anypoint on the grid. When it finds a circuit that is closed, it compares the location ofthat circuit on the key matrix to the character map. The character map is basicallya comparison chart for the processor that tells it what the key at x, y coordinates inthe key matrix represents. If more than one key is pressed at the same time, theprocessor checks to see if that combination of keys has a designation in thecharacter map. For example, pressing the a key by itself would result in a small

letter "a" being sent to the computer. If you press and hold down the Shift keywhile pressing the a key, the processor compares that combination with thecharacter map and produces a capital letter "A."

The character map in the keyboard can be superseded by a different character mapprovided by the computer. This is done quite often in languages whose charactersdo not have English equivalents. Also, there are utilities for changing the charactermap from the traditional QWERTY to DVORAK or another custom version.

Keyboards rely on switches that cause a change in the current flowing through the

circuits in the keyboard. When the key presses the key switch against the circuit,there is usually a small amount of vibration between the surfaces, known asbounce. The processor in a keyboard recognizes that this very rapid switching on

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and off is not caused by you pressing the key repeatedly. Therefore, it filters all ofthe tiny fluctuations out of the signal and treats it as a single key press.

If you continue to hold down a key, the processor determines that you wish to sendthat character repeatedly to the computer. This is known as typematics. In thisprocess, the delay between each instance of a character can normally be set insoftware, typically ranging from 30 characters per second (cps) to as few as twocps.

Keyboard Technologies

Keyboards use a variety of switch technologies. It is interesting to note that wegenerally like to have some audible and tactile response to our typing on akeyboard. We want to hear the keys "click" as we type, and we want the keys tofeel firm and spring back quickly as we press them. Let's take a look at thesedifferent technologies:

Rubber dome mechanical

Capacitive non-mechanical

Metal contact mechanical

Membrane mechanical

Foam element mechanical

Probably the most popular switch technology in use today is rubber dome. Inthese keyboards, each key sits over a small, flexible rubber dome with a hard

carbon center. When the key is pressed, a plunger on the bottom of the key pushesdown against the dome. This causes the carbon center to push down also, until itpresses against a hard flat surface beneath the key matrix. As long as the key isheld, the carbon center completes the circuit for that portion of the matrix. Whenthe key is released, the rubber dome springs back to its original shape, forcing thekey back up to its at-rest position.

Rubber dome switch keyboards are inexpensive, have pretty good tactile responseand are fairly resistant to spills and corrosion because of the rubber layer coveringthe key matrix. Membrane switches are very similar in operation to rubber dome

keyboards. A membrane keyboard does not have separate keys though. Instead, ithas a single rubber sheet with bulges for each key. You have seen membraneswitches on many devices designed for heavy industrial use or extreme conditions.Because they offer almost no tactile response and can be somewhat difficult tomanipulate, these keyboards are seldom found on normal computer systems.

From the Keyboard to the Computer

As you type, the processor in the keyboard is analyzing the key matrix anddetermining what characters to send to the computer. It maintains these characters

in a buffer of that is usually about 16 large. It then sends the data in a stream to thecomputer via some type of connection.

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PRACTICAL NO - 13

AIM: To Assemble A PC.

Theory: For assembling the system follow the steps given below:

1) Unpack.

1.1 Open the cover thecabinet.

1.2 Unscrew the metalsheet on the right sideof cabinet ( on to whichmotherboard is to bemounted ).

1.3 Unpack all the spatesfrom their boxes.

1.4 Collect all manuals and

CDs/Floppies andother accessoriesprovided with thespares.

2) Motherboard.2.1 Place the motherboard

on the metal sheet properly and mark the holes which match withmotherboard holes.

2.2 Fix the risers on the metal sheet and push the spacers in the holes omotherboard.

2.3 Fix the screws at the proper places where you have placed risers on themotherboard.

3) CPU Installation.If the CPU is of SEC type.

3.1 Fix the CPU supporting stands on either ends of the slot.3.2 Push the CPU in the slit and lock the CPU to the supporting stands.

3.3 Connect one end of power cable (a pair of twisted thin wire with two pinconnectors at the both ends ) to CPU fan and other end to the CPU fanconnector on the motherboard .If the CPU is ofPGA (Pin grid Array) type.

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3.1 Unlock the socket by lifting the locking lever.3.2 Place the CPU in socket (match the pins with the holes).Gently press the

CPU3.3 Lock the CPU in the socket by pushing down the lever.

3.4 Apply a thin layer if Heat Sink Compound in the central portion of CPU.( Optional but recommended).

3.5 Place the coding over the CPU end lick it with metal clips in the either side.3.6 Connect the power cord to the fan.

4) Memory Module Installation.Always prefer lower number if slit for installing memory module.

If the RAM is SDRAM.4.1 Just tilt the plastic locking levers outwards in the both ends of slots.4.2 Push the memory module and press firmly so that the plastic levers stand

straight and lick the module.

If the RAM is EDO.4.1 Place the module in a tilted manner in the slit and push it forward, so that

the locking clips make a click sound. Then fix the metal place in the cabinetalong with motherboard, CPU, and RAM.

Fixing the connectors.

5) Before pushing any card or fitting an other device such as hard disk orfloppy drive, connect the COM1( 9 pin D-type male ) and COM2( 25 pin

D-type male ) connectors in their proper place. Also connect LPT( 25 pinD-type female ) port connector in its proper place. Also connect the extraconnectors if any such as display connector (15 pin D-type female ) orsound connector (line out or speaker, line in, microphone and game port )etc. if all things are on board.

6) Fit these connectors at the back panel in such a way that it will notpreferably come in front of the slots provided for cards i.e. in the top.

7) Fit floppy drive in its proper place and connect the data cable and supply to

the drive. If the cabinet has a fashionable slot for floppy ensure that thedrive exactly matches the slot, check this inserting and removing severaltimes. If you find any problem align it properly.

8) Fit CD-ROM in its proper place ( preferably in bottom most slab providedthis makes it easy for operating the CD-ROM ) connect data cable, powersupply and analog audio cable before tightening the screws.

9) Fit Hard Diskensure that it is not too close to the SMPS ( the electrostaticfield produced from the SMPS may prove fatal to Hard-Disk ) or even do

not keep the speaker near the Hard-Disk( magnetic field of speaker maydamage the Hard-Disk ).While fitting the Hard-Disk do not tighten thescrew too much.

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10) At last push all the cards in proper slots.

11) Connect all the connectors such as HDD led, Reset switch, Power led,Power ON switch (in case ofATX power supply).

NOTE:While fitting the motherboard :- While fitting the motherboard on themetal plate do not place the paper sheet below it because the paper sheetgets heated also sheet holds electrostatic charges thus reducing the life ofmotherboard.

While fitting CPU:- In case of SEC type of CPU generally the CPU id

placed on the motherboard in such a way that the fan blows air over themotherboard.

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PRACTICAL NO 14

AIM: Troubleshooting of the printers, memories, monitors and hard

disk.

HARD DRIVES

Modern IDE hard drives are among the more reliable system components,they should run for years, then fail with a whimper or a bang. Most of theproblems that creep up with a hard drive are actually operating system problems.

Physical errors should be easy to spot with any decent diagnostic programthat runs a variety of hard drive tests (including butterfly read). Factory low levelor "rescue" formatters will scrub a drive and prepare it for FDISK no matter howbad the software problems get. The most common reasons for returning harddrives at burn-in are; excessive noise, failure to allow partitioning with FDISK,

failure to remain FDISKed, and various incarnations of dead (doesn't spin up,doesn't seek, system reports HDD controller failure, etc.).

The most important thing to remember about working with IDE hard drivesis to RECORD THE BIOS TRANSLATION PARAMETERS AT BUILD TIME.These parameters are sometimes incorporated in the drive label. SCSI drives areset up as not present in the CMOS setup and are operated through the controllerBIOS. Read the manual. The only jumpers to worry about on IDE hard drives arethe Master/Slave jumpers, which aren't always consistent even from the samemanufacturer.

New systems come with an "Auto detect Hard Drive" option in the CMOS setup,which will restore the drive parameters automatically, and can be used torediscover parameters for drives from older machines.

Older hard drives are not worth repairing, due to the availability of faster, largerdrives costing the same as the repair. The challenge with old hard drives is tryingto recover data that was never backed up before recycling them as bookends.

Old drives that spin up but don't seek are often stuck in park.

Tapping on the drive cover with a screwdriver handle may unstuck the heads andget the drive going long enough to get the data off.

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