Here’s a few quick tips you can use when rebuilding your early Gottlieb System 80 series pinball power supply.

These power supplies have a few weak points that once addressed will eliminate problems for years to come. First is the capacitors. They are 40+ years old and drying out. It’s always a good idea to replace them when servicing your power supplies.

The next weak link on this particular unit is zener diode CR7. As you can see by the burn marks on the board in the photo below, they work hard and get hot.

Whenever replacing parts that get hot I always recommend mounting them high as possible off the board. This will prevent them from burning the board more while allowing more air to flow around the component, keeping it cool.

CR7 is an 8.2v 1watt zener diode 1N4738A. You can get them from your favorite electronics supplier. You can see in the pic below how I mounted the new diode.

I’ve found it’s also good practice to replace the 3 headers on the board, J1-J3. Those round pins suck and I’ve chased a lot of stupid problems because of those pins. While you’re at it, replace the housings and pins on the harness side too. Then you’ll have nice solid connections that will never give you problems again.

I also replace the 4 rectifier diodes for the display power section (CR1-CR4). I use 1N4007 which are nice and beefy and will further bulletproof your power supply.

Once those things are done make sure check all the solder joints on the back of the board. As you can see in the pics below the there’s cold joints on parts of the board besides the connector pins.

When reassembling the PCB to the backing plate you should replace the plastic insulator between the board and plate as well as the mica insulator between the regulator transistor and plate. Clean all surfaces and apply a small amount of fresh thermal compound.

For this last part, someone told me years ago that it’s a good idea to run jumpers between the emitter and base (the pins that protrude through the board) of Q3 and R11. I can’t think of ever encountering a situation where this was necessary. I guess if you really damage the eyelets during disassembly then you’d have to do it.

Either way it doesn’t hurt anything and gives you a little redundancy in case something gets damaged. Some people use small lengths of wire, sometimes I’ll use copper foil tape and make traces and other times I’ll use zero ohm resistors as shown below.

Another thing to note is if you’re diagnosing problems on your game and you see that one of the LED’s aren’t lighting on your power supply, take a battery and see if you can get it to light. sometimes the LED fails and you’ll spin your wheels thinking you’re missing a voltage.

These are relatively simple power supplies and doing these few extra things will make your game dependable for years to come.

If you found this helpful or you learned something then please share it.

‘Till next time, Frank