I recently bought a used HP 6644A power supply (from 1993 or so, a bit over $100 on eBay (parts only/not working)), and am trying to do a quick check-up on it. I have two small concerns that I'm unsure if I should ignore or not:
1) Taking a look at this unit (and also my 6633A), the clear plastic surround of the Y2 capacitor has some small cracks. Should I expect it to explode soon? [see attached cell-phone photo]
2) The transformer hums at 60 Hz. It gets louder when the output current increases. It never get very loud, but it bothers me that it makes a noise while the other units don't. Or... this unit's fan is off, so perhaps other units make a hum, but I can't hear it over the fan noise? Do I need to worry about the buzz? Is it indicative of some other component failing?
Otherwise, it works, and its calibration of voltage and current outputs seem dead on (have not verified OVP or COP). With its output disabled, it outputs about -0.07 V, which I think is normal [I also have a 6633A which outputs a bit of voltage when disabled]. I did have to resolder the output connector (cracked solder joint because there is no mechanical support of the output jack).
Thanks,
Nathan
EDIT: X2, not Y2