D. Sumida and K. Izumi,

 Today we had an engineer visiting from Coherent Japan Inc., Daisuke Sumida, who inspected the controller box of the problematic laser (8102, 8150) for us.

However, in the end, we were not able to spot the faulty part of the laser controller. So the laser controller remains unable to remotely control the crystal temprerature. It is likely that we need to send this faulty unit back to factory for the repairment.

[The inspection]

 Before doing the inspection, we went into the PSL room and disconnected the controller from the rest. Subsequently we brought the laser controller out of the mine and put it on a desk of the prefabricated house at the entrance of the KAGRA tunnel. See the attached picture.

 Sumida-san then opened up the controller box following the instruction document seemingly prepared by the factory. He then pulled out an electronic board which was for the laser crystal tamperature control. If this short-circuit is due to this board, we would observe a high impedance at the BNC input. In fact, he brought a replacement board for such a case. However, removing the board didn't change the input impedance. So, it wasn't due to the electronic board.

 We kept going by performing visual inspection trying to spot an obvious short-circuited point, but no luck. Sumida-san belives that the faulty part may come from the mother board to which the temperature controller board had been attached. Accessing the mother board seems to require removal of lots of components. We need to send this unit back to factory for the repairment. 

After the inspection, we brought the laser controller back into the PSL and plugged all the cables back in. We were then able to confirm that the laser happily emitted some laser light both and 1064 and 532 nm once we switched on the controller box.