Former my 2465A died suddenly


Hello to everybody. I am still fighting with the power supply of my 2465A scope. I began last year and now I don´t know what to do.
I was following inverter troubleshooting procedure. Everything was ok before but now the voltage at the cathode of CR1023 stay low. I connected a power supply to the junction of R1020 and CR1022 and slowly rised the voltage to 28V.
I checked Q1021, Q1022 and Q1040 with my AS4002 semiconductor analyzer and the transistors showed no problem. The same with VR1020.(I got a new one). I unsoldered all resistors and capacitors to check them out of the pcb.
U1030 oscillates when it got 12V. When I connect -- direct to the emitter of Q1022 (shorting VR1020), the votlage on the cathode of CR1023 is the same than of the PS I am using minus the 0,5V.
Does anybody had a similar problem or could somebody please help me out giving me an advise.
Thank´s to all and gratulation for new forum.

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