New ISS outer loop prototype board was modifed and put in. Modification details will be in a separate alog.
PD5, 6, 7, and 8 anode and cathode cables were disconnected from the old transimpedance box under HAM2 and was connected to the PD5-8 cable for the new prototype board. One strange thing about the old setup was that the "LR C" and "LR A" cable that come from the chamber feedthrough were connected to the anode and cathode input of the old box, respectively. Since apparently they gave us a correct signal (no forward bias across the diode), I connected "LR C" chamber side cable to "LR A" rack side cable for the new setup.
I connected PD5-8 cable to PD1-4 input in the new prototype box. We can conveniently switch back and forth between the old and the new by just switching one cable that goes to the "outer loop input" connector on the 1st loop chassis.
I briefly connected the output of the new box to 1st loop, and enabled the servo, but it didn't work. It's not clear if the sign is correct, but there's no way to change the sign externally, I need to open the box. I'll make more measurements next week to see if the sign is indeed wrong.
I connected the old second loop back to the 1st loop.
Cold solder joint in the short circuit protection box.
Initially I was confused with the gain control of the VGA chip in the new box as there seemed to be a factor of 2 missing in the gain control chain. It turns out that PSL people put a small box on the anti-imaging chassis front panel in CER. These boxes are just DB9 pass-through except that all traces have 100 Ohm resistor in series.
Anyway, pin1 of this box, which corerespond to the positive leg of the VGA gain output, didn't have any signal coming though. When I opened the box I was baffled to find no error, but it turns out that just a tiny amount of bending would cut the connection. I re-soldered the resistor and the connectors, and now it seems to be good.
But this is not the reason why the new servo didn't work.
This is the box that was fixed.
There appears to be an entry in DCC for S1201761, but I don't have permission to view that.
Update:
Vern has the permission to view S1201761 and has found that the corresponding D document is D1102351, aLIGO PSL DAQ DB9 breakout. I can view that D document without problem.
The summary on that page doesn't sound like it was for short circuit protection as I have initially guessed, but an in-line damper against high frequency oscillation of AI output amplifier. I don't know if we need this, but if we do, I'd strongly suggest to improve the mechanical design (or move them inside the AI chassis).