HP 5300B Measuring System Power Supply Whine

[Proton Peasant]

Howdy folks,

I purchased a HP 5300B with a 5308A 75MHz frequency counter (non-op) with the intention of repairing it and giving it a home on my bench.

There is an audible whine coming from the power supply area of the 5300B, so I checked over the power rails, electrolytics and tantalums.
I did have to replace a few, but it made no difference.

So I found a PDF of the manual (available through Keysight), and stepped through their troubleshooting flowchart.
They even make mention of the whining, so it apparently is a somewhat-known issue.
These units have a blocking-oscillator based PSU, with some half-wave rectification to give +/- 17V, +/- 5V, and +3.5V.

In the flowchart one of the tests is to apply +6V across the filtering capacitor and probe the collector of the switching transistor.
When I performed this I found almost double the peak-to-peak amplitudes specified (see image below).
Pulling the transistor and testing it with a cheapo component tester didn't raise any red-flags, though.

I continued through the power supply checks in the manual, testing nearly every component mentioned out-of-circuit to no avail.

Either the trouble is more subtle than expected or I bought a lemon.
Does anyone have any ideas or experience with the 5300B measuring systems?

If there are any other details that would be helpful, let me know.

Manual via Keysight:
https://www.keysight.com/ca/en/assets/9018-05900/user-manuals/9018-05900.pdf

Attached are:
- a picture of the circuit board with the power supply section outlined in red
- A capture of the blocking oscillator transistor collector voltage (5V/div, 0.1mS/div)
- PNG of the power supply schematic, again the full manual can be had through the Keysight website.

Best,
Proton

[KE5FX]

I'm not familiar with the 5300B system, but that hardware will look very familiar to anyone familiar with HP's atomic (Rb and Cs) standards from the same era.  Short answer: yes, they make some racket, and it's almost certainly normal if the voltages are in spec.

Have you checked the ESR of all of the filter caps associated with the circuit?  That could account for some of the noise.