Sorensen XT 7-6 Repair Help

[ar619]

Hey EEVblog readers -- I just purchased a used Sorensen XT 7-6 power supply in unknown condition. The physical condition of the unit looks great, but I have observed two issues upon powering up the unit and measuring the output:

1) There is an audible buzz that come from the unit. In fact, you can feel vibrations if you touch the bottom of the unit. I'd assume it's coming from the transformer.

2) The bigger problem: the output voltage is oscillating at about 130kHz (FYI, I'm in the US 120V/60Hz mains). The mean value of the voltage roughly matches the current voltage setting of the power supply with peak-to-peak oscillation of roughly the same magnitude (i.e. Vpp increases with the output voltage setting). See the attached image for an example with power supply set to 3V.

Given these clues, does anyone have a suggestion as to where to start debugging?

The following post is regarding a similar unit and has links to schematics and manuals.
https://www.eevblog.com/forum/repair/sorensen-xantrex-xt-15-4-power-supply-repair-calibration/msg1415014/#msg1415014
In that case faulty capacitors were suspected. Given the specific characteristics of the issues I'm seeing, I'm wondering if there are a few specific capacitors that I should look into first (instead of taking them all out)?

Finally, (I know I'm asking a lot) is there any chance fixing problem (2) will resolve problem (1)? Or is it more likely that (1) is just due to an old transformer that needs to be dealt with seperately?

Thanks for any help!

[ar619]

Pinging this thread...let me know if there is other useful information I can provide.  Haven't had a chance to actually open up the device and start probing yet.