Keita and Kiwamu

In order to investigate the large cross coupling issue in OMs (alog 13575 by Dan), we checked the OM driver electronics.

We found that the OM1 and OM2 coil driver Vmon are not properly functioning. However, this does not explain the cross coupling that Koji and Dan experienced.

Anyway, these two coil driver chassis (S1200614 and S1200612) need to be swapped at some point.

(some details)

When we started looking at the OM screens, we immediately noticed the LL voltage monitor of OM1 and OM2 displaying anomalously high voltage while the zero DAC voltage were requested. OM1_LL showed approximately 23000 cnts and OM2_LL showed approximately -23300 cnts. Even so, these channels were still sensitive to the bias we sent through the DAC -- we could change the readout values by changing the biases. But they did not go to the other sign in the readout voltages.

We then went to the electronics room to check out the analog circuits. Looking at DB9s' signals for the Vmons by inserting a 9-pin breakout board, indeed we saw LLs exhibiting a funny voltage. LL of both OM1 and OM2 were at -14 V when the zero DAC voltage were requested. Then we went to the AS port rack to check if this is also the case for the actual drive signals. However the drive signals looked healthy on both OM1 and OM2. We checked this by looking at the signals at the input of the satellite amplifiers. All the signals could swing from -22 to 22 V as we changed the DAC voltages.

We are concluding that the Vmon part is not properly functioning in the OM1 and OM2 coil drivers. But, since the actual drives are healthy, this issue is independent of the cross coupling issue.

By the way, the OM3 coild driver looked healthy and its Vmon looked fine. So we did not check them.