Hantarex US250 power supply squealing

This is a follow up to my previous thread about my Electrocoin 6-slot Neo Geo in distress. My MV6 board now boots and works with 3/6 slots. The Hantarex US250 power supply power supply turned out to be a pain though.

The US 250 supply previously made a high pitched whining sound and didn't give power. After reflowing all solder joints the supply worked perfectly fine when disconnected from the game, but plugging in the MV6 board makes the beeping sound return, even though the game plays okay.

Yesterday I replaced all the supply capacitors except the big one with Nippon 105C low esr caps. The problem remains the same: a working arcade game but a screaming power supply.

I'm a bit stuck here. Can anyone give me some advice on how to proceed?

It's most likely that you need to replace the transformer. Also low ESR caps can cause addition oscillation in a PSU not originally designed to use them.

bustedstr8 said:

It's most likely that you need to replace the transformer. Also low ESR caps can cause addition oscillation in a PSU not originally designed to use them.

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Since it's a switcher, most caps need a low ESR. The rest is 78xx series regulators so the caps should be fine. Also there is no change since the replacement.

Right now I'm mostly in doubt whether it's something in the power supply or that the MV6 is pulling crazy amounts of current.

Could just be coil whine from stress. Though if you can, I'd replace all the coils and see what happens then.