HP Elitedesk SFF Power Supply Noise

[M.najari]

Hi
I bought a used HP mini PC Elitedesk 800 G3.
Everything works correctly, but has a problem with PSU.
When system is off or standby, there is a high frequency noise from PSU.when system is on, noise decreased.
Disconnected PSU from motherboard has noise too, and when I disconnect power source, noise increase and continue for about 10 seconds and then cut.
Power Supply is 180W made by Chicony.
I changed most of electrolyte and ceramic capacitors from PSU board, but nothing happened and transformer continue to buzzing.
I attach PSU boards Pic and highlight replaced capacitors with Red Arrow and tested capacitor in good condition with Blue tik.
I'm so confused what is the problem and why noise not gone by replacing most of board's capacitors.
Please help...
Thanks.

[Whales]

This is known as coil whine and it might be considered acceptable by the manufacturer.

I'm not sure how to fix it (other than changing the switchmode controller or the transformer, both of which basically require designing a whole new power supply).  Maybe you could inject epoxy into the transformer windings so they are not loose?  Not sure if that would even work to be honest, perhaps they don't have to be loose for the whine to be audible.

My power supply from 10 years ago (a blue Vantec ATX PSU) had annoying coil whine, combined with coils in its fan that sounded like an idling diesel.  My rightmost monitor hisses when in standby mode (probably due to pulse skipping acting a bit like spread spectrum?) and my leftmost monitor has a loud whine if you run its backlight at anything other than 0% or 100%.

[M.najari]

I pressed the ferrite core of the coil with my hand in different directions, but in the best case, 50 percent of the whistling sound decreased and it does not seem that the problem is from the looseness of the core.

[Whales]

The copper windings are probably on a plastic bobbin, not on the core directly.  Those windings will always be loose to some degree (unless potted in resin/epoxy) and may vibrate on their own.

(Obligatory: be very careful poking this transformer, it has 400V at very high frequencies that might conduct through things you expect to be insulators.  Poking it with a finger might not be wise)

[BrokenYugo]

Some sort of electrical/transformer varnish maybe?

[M.najari]

Thanks for the warning @Whales
Most of the time, the problem of whistling transformers is solved by replacing the capacitors. The sound of the whistle continues after the power cut until the capacitors are completely discharged. It seems unlikely that it is due to a loose coil.

[Whales]

You mean the large black electrolytic capacitors, approximately 400V rated?  Hmm, I guess they could cause this symptom if they're very bad and old (high ESR + low capacitance).  They won't be the only possible cause of these symptoms, coil whine can and does occur even with good caps.