Because the X-ray anode preionizer system used the same high voltage control design as thyratron discharging. We exchanged the SCR phase controller ERATRON FPE 202 D30 for troubleshooting.
This time, I can control the H.V. pulse for thyratrons, but cannot control the x-ray anode H.V. pulse. We confirmed that SCR controller cannot be run well. When the H.V. pulse modulator set scroll was tuned from 3.0 to 6.0, the current waveform at transformer primary was followed to change. The voltage meter showed the H.V. changed from 5 kV to 15 kV.
I also monitored the transformer secondary current I_mon and SCR firing angle. We finally concluded that SCR firing phase controller was not well, Mike helped to replace some problematic chips. ERATRON has been not existed, it's impossible to buy the same controller. The similar controller may be found to replace. A company named PLC Center provide repairing service. We would like to send this block to them for repairing if we cannot do it.