User:Scott Hively/pinball/black knight/bk electronics

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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.

Power Supply

These original power supplies are very inefficient. They generate a lot of heat.
With sketchy connectors and dried-out capacitors, this thing is generating some noisy and out-of-spec voltages.
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.

Original BK PS, installed
Original BK PS, removed

This is the original power supply. Just look at that heatsink on the voltage regulator!

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. Some years ago 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.

New connector

Here's the new connector compared to the old one.

New power supply installed

And here's the new one, installed and powered. Sexy!
LEDs behind the fuses and by the voltage test points are sooooooooooooooo nice.
You can see the new 2-pin connector on the right, and the new 12-pin on bottom.
I did not replace the GI (general illumination) connector even though it looks burnt. I have replaced all the old incandescent #44 bulbs with LEDs. The connector is still making good contact and now only caries a fraction of the current. It'll live.


The CPU board has a 40-pin interconnect with the power driver board. This interconnect is essential for the operation of the machine and is sensitive to poor connections. At 40 years old, the pins are losing their tension.

CPU board

This is the CPU board.
The lower left corner of the board once had a battery holder installed. The batteries had leaked so I installed an off-board battery holder. (That's what the black / red wires are going to.)
Now, the alarming thing here is how black the board is at the bottom-left. This is not due to battery leakage. It looks like it has been in a fire! I can find no real damage though.
Along the bottom edge of the board, you can see the 40-pin interconnect pins.

power driver board

I post this picture here just for reference.
Along the top is the 40-pin through-board female connector that connects to the CPU board.
I replaced that relay on the left a few years ago. It switches power to the flipper circuit.
The bottom-right of the board has some toasty resistors and transistors. I'll be replacing these soon.
Notice, there are no scorch marks in the upper-left corresponding to the scorch marks on the CPU board. Also, there are no scorch marks on the back of this board. Is it possible this is not the original board?

Backbox scorch marks

Wow! Behind the driver board are scorch marks the correspond to the marks on the CPU board. I think the power driver board had a flame-out and was replaced at some point before it came to me.

New interconnect

Here is a closeup of the new interconnect connectors installed.