I recently purchased this 6624A linear PSU. It is a 4ch supply and 3 of the 4 channels work fine - ch 4 reports OVERVOLTAGE and the output when off is about 620mV or so. At the moment, I only need 2 channels and 1 is a backup. Repairing the #4 channel is a skill-builder challenge and a nice bonus if I can sort it out.
So far, I have done the visual inspection and started troubleshooting from the output stage backwards - thinking that maybe someone back-fed it. The first real slow down has been the service manual I have found appears to be for a newer model. While it is close - there are enough differences that it is making a challenge to figure out what is what schematically. The way this unit is configured is that each output channel is it's own self-sufficient PSU fed from a big transformer in the middle. This makes comparison troubleshooting rather straight forward and I have found some disparities between the working and non-working sections. Without the right schematic, it is hard to get down to a specific component though. There are a few custom parts and the output transistor stage is in a module that may not be economically viable to repair. The goal is to isolate the easy parts like voltage references, OP amps, discreet transistors, etc that may be damaged.
Does anyone know a source for older service manuals that may cover the serial number range that I have in front of me?