https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Pre-DCS_Sound_Board_Issues

Take a look at the schematic. It's on page 15 (sheet 2 of 2 for the Sound Board). If your fuse is blowing immediately without any trigger (i.e. pretty much when turning on the machine) then there's probably a direct short from the supply power to ground. You should probably measure to check there's a direct short and then test (or remove) components until you find the short. Shotgunning does work but it's not efficient.

You've check the diodes. If after you've had fun with the capacitors and you still have the short go for the ICs. That would be the LM7812 and LM7912 voltage regulators as well as the LM1875 amplifier.

If you don't know how to read a schematic you should say so. I don't know your knowledge level but I assume if you are de-soldering and replacing components on a printed circuit board you know how to read a schematic.

It's ok to not know something. That's when you ask for help. If you're willing to read and learn I'm willing to point you in the next direction to the limit of my knowledge and experience.

Those pins should be tied together. Picture attached. Pins 1 and 2 connect to one end of the VCT from the transformer. Pins 4 and 5 carry the other end. Pins 6 and 7 connect to the center tap - which is why it is connected to the power ground.

Check the diodes (I believe you stated that you have already done this). Check the capacitors (unlikely but possible). Check the ICs. For the ICs you will need to know which pins connect to where. The schematic labels the pins for the amplifier but it does not label the pins for the voltage regulators. You can find data sheets to acquire this information.

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