In the morning, I checked the HIPOTRONICS 30kV DC Power Supply. When this equipment was open, the voltage monitor showed 30 kV as I set the output to full scale. When I took out the output cable, I found the cable end was burned because of the arcing. I contacted Hipotronics company, they will charge us $190 for a 3 feet cable and it will take a week for delivery. Fortunately I found a similar cable in the cabinet, I cut it to fit the power supply. But it's weird that click sound still has been heard inside the oil tank, I did not find the key to make the x-ray anode trigger failed.
The only part I have not checked is the 150 kV cable connector with the capacitors, I already drained the cap oil tank. I will check the connector tomorrow.