Uehara, Kohei Yamamoto

As I reported before (5691), we had the problem on the SLOW OUT & TEST1 of EXCITATION B. 

(SLOW OUT)

-As planed, we checked if the latch circuits were broken, and expectedly four out of six were. We replaced them and made sure that new ones functioned. 

-Then, the signal reached SLOW OUT only with the bypass and no signal without it. 

-Found that the operational amplifier, U53, were out of order. 

-After it was replaced, we came to get the signal without the bypass. But once we activated the filters at the SLOW PATH, no signal came out. It was true of the COMMON filters.

(TEST1  of EXCITATION B)

-We found that the switches, U41, was broken so strangely that we could find it with our eyes. We also replaced the switch. 

-We could get the signal at TEST1 of EXCITATION B and, at the same time, all the switches on COMMON and SLOW path came to function as well. 

After these examinations, the common mode servo finally works well. 

As often said, the power line can be thought as the factor which caused these problems. But if so, more circuit elements can get broken, not only the operation amplifier. 

Because the broken elements are all related to the BO port or near the switches, we suspect that these are attributable to the BO cables. As I reported (5662), when we examined the binary signals with the checker boards, we found the weird offset of 6[V]. 

Last week, we put the servo in the rack in PSL room, but when we install the servo again in PSL room next week, we plan to put the servo on the ground and insert the checker board before the BO cables are connected as done for the same kind of problems before (5066). 

Circuit Diagram

https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/0035/D1503567/001/D040180-F.pdf