User:Scott Hively/pinball/black knight/bk electronics
First thing to note is this machine was manufactured in 1981. With age, electrolytic capacitors dry out, plastic connector housings become brittle due to heat / UV / age and electrical contacts oxidize.
And while Williams was innovative in pinball game design, their electrical designs are a bit suspect in a few areas.
These original power supplies are very inefficient. They generate a lot of heat. Just look at that heatsink on the voltage regulator!
I have decided to replace the board with a modern after-market replacement. I will rebuild the original and have it as a backup or sell it.
This is the original power supply.
Notice the darkened connectors. If Williams needed more current than a connector could handle, they would use multiple pins. This works great for a while until one of the pins has a bad connection, then the others heat up and they begin to fail. Vicious cycle.
The fuse holder in the lower-right corner was badly corroded. The fuse holder would make bad contact, get hot, and de-solder itself from the board. I installed an off-board fuse holder. That's the grey wire you see coming off the board.
Also, the 2-pin connector at the bottom-right had the yellow/black wire soldered to the back. This wire is then wire-nutted to the original wires. This was how I found it when I bought it. I'm assuming the male connector on the wires got toasty so someone just soldered wires to the board.