I checked the x-ray cathode trigger box this morning, and measured the output voltage of transformer. I did not find anything wrong, but the cathode pulses was not good. There must be something wrong, the only part was not checked is thyratron filament voltage.
I measured that voltage, which was 2.7 V. It's lower than the normal value of 6.3 V. From the circuit drawing, this power was provided by M04 Low Power Supply. Please look at the attached picture, the 6.3 V DC is sent to M01, M02 and M11. M01 and M02 for rail gap, M11 for x-ray cathode. It may be two possible cases to decrease the low voltage, one is the thyratron of M01, M02 and M11 not working well, the other is the rectifier diode breakdown. I disconnected the diodes D7-D12 to check, and found D7 and D9 were totally breakdown, so the output voltage dropped to 2.7 V DC. This caused the thyratron CX1585 unstable, which finally effects the x-ray cathode pulses. I think the damaged diode is the main part to make the whole system failure. I did not find any replaced diodes in the lab, the electrical shop was closed when I found the problem. I will ask Mike to find the diodes ECG 5912 or order them next Monday. I hope the system would be run well after I replace the diodes.