GLAST LAT Project May 28, 2004

R. Johnson Tracker MRB, NCRs 107 1

GLAST Large Area Telescope:GLAST Large Area Telescope:

Tracker SubsystemWBS 4.1.4

MRB Concerning NCR 107

Robert JohnsonSanta Cruz Institute for Particle PhysicsUniversity of California at Santa CruzTracker Subsystem Manager

rjohnson@scipp.ucsc.edu

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

GLAST LAT Project May 28, 2004

R. Johnson Tracker MRB, NCRs 107 2

NCR 107NCR 107

• Test failures on two MCMs at +60C.• MCM Serial Numbers 366 and 592• Nonconformance: both MCMs had some event-data (from charge

injection) read-back errors only when reading to the right-hand side and only in the +60C test (they were fine at -30C and 25C).

• We found that the errors from SN-366 went away if the VDD voltage is raised to 2.65V, but the errors from SN-592 did not.

• We tried some other relevant temperatures as follows:– Tracker Acceptance Test Limit:

• 35C: Both function perfectly.– Tracker Qualification Limit:

• 50C SN-366 functions perfectly but SN-592 has errors.

GLAST LAT Project May 28, 2004

R. Johnson Tracker MRB, NCRs 107 3

Root Cause, etc., etc.Root Cause, etc., etc.

• Suspected root cause: – no good ideas so far.– The MCMs are in burn-in and have not been studied any further.

• Impact to inventory: minimal to worrisome, depending on how often it recurs (so far 2 out of 48 flight boards, no preproduction boards).

• Schedule impact: none so far.• Recommended action:

– Complete burn-in and final test on these units.– Put them into MRB storage, but make them available to the

Tracker team, according to work orders, for additional study to try to find a root cause (or at least where the errors occur) and possible corrective action.

– If possible, test at temperature with flight-like C0 cables (no connector savers) when they become available.