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HP8563E suspected PSU problem causing LO spurs

Question asked by pjh on Apr 8, 2015
I have a clean 8563E, with about 20,000Hrs run time, which is functional in all respects except for a couple of spurs at around +/- 35kHz offset:

+/- 32.5kHz offset: relatively "clean" spurs at around -70dBc (N = 1)

+/- 36.8kHz offset: a few dB lower, having 100Hz AM (twice mains frequency, I'm in the UK) with roughly 10dB depth.

This has the whiff of an SMPS problem, which will be the first area I'll be looking at, but it would be helpful to know whether this is a common fault with a likely cause. I guess replacing all the electrolytics in the PSU regardless of state might be a good plan while the lid's off? 

I have the March 2001 Service Guide. Is there any other documentation I should have before starting?

Edited by: pjh on Apr 8, 2015 7:19 AM  (s/36.8Hz/36.8kHz/)

Edited by: pjh on Apr 8, 2015 9:05 AM   clarification: In UK so 50Hz mains.