Gottlieb’s Jacks to Open capacitor tip.

One of the main causes of problems for any electronic device, pinball machines included, is dried out electrolytic capacitors. When capacitors fail they tend to go short. I’m sure your familiar with the kinds of problems electrical shorts can cause.

Since many of these games are 30-40 years or more old, it’s a good idea to replace caps as a preventative maintenance procedure. There is one caveat here though. The caps made in the 70’s and 80’s were better than the ones made today. If the capacitors you’re replacing lasted for 40 years, it’s highly unlikely that the replacements will last another 40 years.

With that said, there’s a chance you’ll be replacing caps that are still good. If you have access to an ESR meter, you’ll be able to tell caps that are failed, or close to failing from ones that are still good.

In most cases though it’s better to replace them considering many failed caps can leak and cause damage just like alkaline batteries. You will see this on Data East pinball power supplies particularly.

On this Data East pinball power supply you can see the start of corrosion damage on the solder mask leading to the diodes.
Data East pinball power supply with leaking capacitor and board damage

Filter capacitors will tend to be in the high microfarad (uf) range, something like 10,000 to 25,000 or more. Linear power supplies need a high uf value to smooth out the “wavy” DC voltage rectified by the bridge rectifier.

If you don’t have a high enough value cap on hand you can tie several caps together in parallel as long as they meet the voltage requirements. Connecting them in parallel means tying the positive leads together and tying the negative leads together then connecting them to the circuit. Two 10,000uf caps in parallel will give you a total of 20,000uf of capacitance.

Data East did this on many of their power supplies. They will typically have four 4,700uf radial caps in parallel. You can replace them with a single 18,000uf axial cap easily enough since the mounting holes for it are there.

Data East pinball power supply with four 5v filter capacitors in parallel
Data East pinball power supply with single 18,000uf primary filter axial capacitor

I did the same thing on this Jacks to Open. There are two 6,800uf radial caps wired in parallel on the transformer board. I replaced it with a single 18,000uf axial cap. I know that 6,800uf X 2 is 13,600uf and I put in an 18,000uf cap which is 4,400uf more.

Gottlieb Jacks to Open pinball machine transformer board
Gottlieb Jacks to Open pinball machine transformer board capacitor detail showing 2 6,800uf caps wired in parallel.
The 18,000uf axial capacitor that’s going to replace the two radial caps.
The new capacitor wired in and mounted to the board with 8inch mounting cable ties.

You can account for at least a 10-20% tolerance range. This means a caps actual microfarad value can be upwards of 20% higher or lower than its stated value. When it comes to filter caps having that much more capacitance makes zero difference. I just wouldn’t go lower than what the factory put in.

There may be times when you may not be able to do this such as in monitors or audio circuits. When in doubt just replace with the same value you’re taking out unless there’s a service bulletin updating the design.

Hope you found this helpful, until next time. Frank

Be the first to comment

Leave a comment