LATC Verify Error

1. LATC Verify Error • Issue • LATC verify errors observed on second cold plateau • The LATC reported error was in TFE (5, -x7, 23) • Calibration mask has bits set that should be clear • Investigation • There were a total of 11 failures out of 38 LATC verify attempts (in a total of 22 runs) • 6 at the run start LATC verify and 5 at the end of run LATC verify • Pattern clearly indicates a read error rather than a write error • 10 successive LATC dumps resulted in 4 correct readouts and 6 incorrect readouts (3 different values) • This set of errors was followed by 33 runs (66 LATC verifies) with no errors • An additional LATC verify error was seen at the start of the ramp to ambient • Traced to a known register readout sensitivity of the GTFE (does not affect science data) • Saw similar issue at LAT level test on NCR 971. In that case, the problem was in GTFE (0, -x6, 20) • Sensitivity increases at low temperature (as was seen in NCR 971) • This plateau started physics runs with the tracker towers colder than at any other plateau • The last error in the first series occurred at 3 degrees (average of all cable temperatures), the error at the start of the ramp to ambient was at 2.5 degrees • LAT TVAC temps were 5.7, 10.7, 9.5 and 8.5 • The first SC cold plateau was several degrees warmer, but still had some runs below 3 degrees • Observed temperature range is a test only condition • Based on the TV data and on-orbit predicts, the temperature (average of all cable temperatures) should be at or above 11 degrees

2. LATC Verify Error (Continued) • Resolution • Two options available • Use as is • Use as is, include in ignore list so repeats will not impact operations (recommended) • In-orbit impacts • If the TFE is not put on the ignore list and the sensitivity increases with age then some physics runs will not start until the TFE was put on the ignore list • If the TFE is put on the ignore list there will be no impact