Power Supply Repair of Adam Sub 7 Subwoofer

[Magnum]

Hello,
I have a Adam Sub 7 Subwoofer where the Power Supply died.
It has one board with the switching Power Supply and also the amplifier for the Sub on it.

I don't know much about switching power supplies, but found a shorted diode on the secondary side and the controller chip (the big one with the heat sink) seems to have a problem. A resistor (120k), which is connected to it, gets quite hot (>70°C), and on one leg of this chip the solder melted.
Unfortunately they removed all markings from that chip. So I don't know what it exactly is and where to get it.

I isolated the power supply from the rest by removing the secondary diodes and injected +-20V to the board and everything works fine. My plan is now to disable the original PS and install another PS with +-20V. The question is, how many watts the new PS should have (when testing the board it needed less than 500mA to drive the sub at a quite high level) and what kind of PS I should use. As it is for audio, is there anything I should care about? Also I have not found a PS with +-20V, so I plan to use two 24V supplies, turn the output voltage down as much as possible (around 21V) and connect them together. Any ideas what I else should think about?

Many thanks for your help. The sub is quite good and costs around EUR 400,- so I would like to make that (cheap) repair.

Magnus

[Audiorepair]

That black gunk all over the PCB is the type that goes conductive and corrosive, so you may want to remove any on the parts of the circuitry you are keeping.
It's possibly what killed the PSU in the first place.

[Magnum]

Thank you for the info, I will remove that stuff.

I am still wondering about the 20V power supplies I should use. I found two 12V voltage regulators on the board, they are rated with 700mA (positive) and 1,8A (negative). So I assume, that output ripple won't affect the quality too much, as it will be regulated again anyway. And 1,2A at 20V should be enough. Or am I wrong?