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Gamma-ray Large Area Space Telescope. GLAST Large Area Telescope: Tracker Subsystem WBS 4.1.4 MRB Concerning NCR 107 Robert Johnson Santa Cruz Institute for Particle Physics University of California at Santa Cruz Tracker Subsystem Manager rjohnson@scipp.ucsc.edu. NCR 107.
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Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Tracker Subsystem WBS 4.1.4 MRB Concerning NCR 107 Robert Johnson Santa Cruz Institute for Particle Physics University of California at Santa Cruz Tracker Subsystem Manager rjohnson@scipp.ucsc.edu
NCR 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.
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.
