HP 8643A Frequency Generator Won't Power Up

[Chris K]

I bought this about 6 months ago and the only thing wrong was the memory NiCad battery being dead. I did a bunch of things with it including trying to replicate the sweep generator output of my HP8600/8601 combo for aligning vintage TVs only to find in the 25MHz range, all it could do was sweep 2x per second. Not exactly useful if you're trying to tweak an alignment trace on a scope. Anyway, it's totally dead. I know these units have problems with bad caps on the power boards and I watched Bob's repairs on his 8662 but my unit has a differently designed power section and my God, is it user UNFRIENDLY for service. I saw a YT video that the place to start is the safety cap on the AC line and mine is the suspect, epoxy encased brand (Rima???) referred to. Although the design is different, anyone have any ideas on what else to look for or what the most common power section fail component is? None of the boards look damaged or burned and there's no obviously damaged or vented cap on the top. In fact, there're not a lot of non-electrolytic caps in this circuit anywhere. I don't see anything like the capacitor Bob found that was open and the key to powering up the 8662. BTW, the cooling fan never worked on it either. The fan is good...I tested it with a 24V DC power supply but hearing the fan running noise for the first time, I don't think it was ever running.