J. Kissel, F. Clara, E. Hall The commissioning vanguard had discovered that a portion of the ITMX M0 Top Driver's Binary Input/Output (BIO), which is control of the low-pass and test/coil enable switches, was malfunctioning a few days ago (see LHO aLOG 17449). This afternoon, Fil, Evan, and I ventured into the CDS highbay to diagnose the problem. After a cable-to-cable swap at the coil driver between ITMX M0 F1F2F3SD BIO cables and the ITMY R0F1F2F3SD BIO cables, and cycling both suspensions' top mass digital control and readbacks, we identified that *one* bit (the F1 bit) of the ITMX M0 F1F2F3SD BIO remained stuck (with the otherwise functional ITMY cables). This made us suspicious of the BIO chassis. However, due to time constraints, we couldn't diagnose further. Instead, we restored the nominal configuration -- and this FIXED the problem. Thus, happily, the problem is gone and all of ITMX driver channels can switch as expected, but, sadly, we don't know why our cable Chinese fire drill fixed the problem. ----------- Other details: Follow along using pgs 8 through 14 of D1100022 where the BIO connections happen. Remember that the top mass cabling -- even through the SUS have 6 OSEMs on the main and reaction chain -- is grouped in groups of four OSEMs. For a given QUAD, the break down is Set 1: M0F1 M0F2 M0F3 M0SD Set 2: M0LF M0RT R0LF R0RT Set 3: R0F1 R0F2 R0F3 R0SD thanks to the mechanical arrangement of the cabling in vacuum (see T1100327). What we saw initially: When we requested to switch the M0 "coil driver" (the main chain uses one-and-a-half top drivers) filter state request to go from State 1 to 2, it switched only the M0F1F2F3SD set, and it switched the test/coil enable bits instead of the filter state. This was reproducible over many attempts. All other functionality -- switching ITMX R0 state and test/coil enable was functional -- indicating a problem only with this cable/OSEM set. We confirmed that all cables were connected and secured screwed in as designed in D1100022 before doing anything. We swapped the cables at the coil driver, namely (on pg 9 of D1100022) we exchanged cables CAB_L1:SUS_ITMX-102 and CAB_L1:SUS_ITMX-103 in the SUS-C5-37C top driver position/chassis with the CAB_L1:SUS_ITMY-100 and CAB_L1:SUS_ITMY-101 in the SUS-C5-39C top driver position/chassis. With all cables connected in this fashion, the ITMY M0 and R0 BIO was entirely functional bhaving as expected. The ITMX M0 and R0 BIO was *more* functional, in that switching the filter state request actually switched the filter, EXCEPT that the F1 LP bit remained stuck. We then quickly assumed that this series of events was symptomatic of a problem with the ITMX BIO chassis, but we ran out of time to create enough test scenarios that we're confident. Running out of time, we re-exchanged the cabling, restoring everything to how it was, and to how its laid out in D1100022. However, after toggling the ITMX and ITMY BIO switches again, to confirm that functionality had been restored to ITMY and the same broken behavior was present on ITMX, we found that all problems had been fixed. YUCK. Well, YAY, but... YUCK. We'll keep an eye on this BIO chassis to see if it goes screwy again, but for now we consider the problem (dis-satisfyingly) fixed.