Summary of Cornucopia of MC1/MC3 Top Mass Problems This Week (Rahul, Camilla, Cheryl, TJ, Fil, Dave, Erik, Sheila and Keita)

This week we had three different problems, all related to MC1 and MC3 top mass. Two of them seem to have been fixed, one is yet to be solved. Since we have alogs scattered around all over the place, here is the summary.

Problem 1: MC1 top T3 analog LPF could not be turned on: Solved

This channel is on the driver chassis that handles MC1 M1 T1, T2, T3 and LF.

Cheryl found that MC1 top T2 and T3 were going crazy: alog 57094

Later it was found that T3 coil LPF wasn't switching, causing loop instability: alog 57103

Power cycling h1sush2a and related chassis fixed the problem for a short while: alog 57113 but the problem almost immediately came back.

Fil replaced the driver: alog 57140

It's been running OK since then.

FRS: https://services.ligo-la.caltech.edu/FRS/show_bug.cgi?id=16045

IIET: https://services.ligo-la.caltech.edu/FRS/show_bug.cgi?id=16047

Problem 2: MC3 top T2 coil BIO readback is incorrect: Not solved, but it's just a readback issue, control is good.

This channel is on the driver chassis that handles MC1 RT and SD as well as MC3 T1 and T2.

Cheryl noted that BIO screen for MC3 top T2 coil showed that the test input is enabled for this one. Later it turns out that this has been going on since August 2019: alog 57124

It's clear that the drive signal for T3 coil from DAC actually makes it to the coil, therefore TEST is not enabled: alog 57144.

Fil checked the analog BIO readback signal coming to the BIO input on the floor was correct. BIO input chassis was replaced, then BIO card in the IO chassis, but the readback is still bad: alog 57158

As of now, this BIO bit is still bad and we're scratching our collective head. This is not causing any control problem as this is just a readback issue.

FRS: https://services.ligo-la.caltech.edu/FRS/show_bug.cgi?id=16111

Problem 3: MC3 top T3 coil output is about 6dB weaker than others: Solved

This channel is on the driver chassis that handles MC3 M1 T3, LF, RT and SD.

TF from T3 COILOUTF to voltmon, fastimon and noisemon are all about 6dB lower than others: alog 57144

Damping loop shape measurement comparison shows that this is a problem that didn't exist in the past:alog 57155.

Fil found on the floor that one leg of the differential analog output from the AI chassis was bad for this coil, swapped the AI chassis, and after that the problem was gone: alog 57167. Since we were worried if something similar was going on in any of the HAM2 HxTS, Rahul measured the coiloutf offset VS voltmon and confirmed that all coils of all stages for MC1, MC3, PRM and PR3 are working consistently.