Here was my setup for working on the power supply on the test bench. I’m powering it from a variac, and I built a dummy load to provide the minimum output loading that the power supply needs for proper regulation. A high voltage differential oscilloscope probe is quite handy for working on stuff like this. I did get the power supply to generate power after I replaced the main switching transistor, but it still has trouble in its control loop that keep it from regulating that power. The shorted power transistor was probably a secondary failure after the regulation circuitry developed problems.