Another Tek 7603

[Zenwizard]

Working on repairing and calibrating a bench scope for the lab and went with a 7603 for the large screen. I am having some trouble with the 130 Volt rail. All the other power supply rails are in spec but this one is running at 145Vdc. the weird thing is there is 4Vp-p ripple on the rail. I have checked the parts in the 130V section and found a blown out zener it should have been 43 V it was not going in to reverse till 57V also found some resisters that were off in value. I got them replaced. I am starting to suspect C806 which is the bulk filter cap for the 80V feed part of the 130V rail. Or is there any where else I should be looking?

[capt bullshot]

I'd suppose to check the transistors Q852 and Q850 and the few resistors and diodes around them. The circuit looks quite simple, Q852 does the regulation part by comparing the voltage from the R855/R856 divider to the +50V (as reference). Q850 is the pass element. Since the output voltage is too high, I'd suspect one of the transistors gone short C-E, the divider resistors drifted, R853 failed open. The 43V zener  is used for startup / protection, not conducting in normal regulation, so it may have failed as a secondary failure.
The 4Vpp ripple would be the result of Q850 fully turned on or shorted. In case C806 was failed (dried out, lost capacity), the ripple would be way much higher.