Pinball PCB Drive Transistor Quick Test

Pinball PCB Drive Transistor Quick Test
Before installing a suspect MPU or driver board into a game or your test bed, a quick test with your DMM can save time and effort. Shorted transistors will show continuity to ground. A normal reading would be "open". Anything else indicates an issue with the drive transistor.

[@Evergreen085]

You saved me! THANK YOU!!! I have a Tales From The Crypt and I'm learning so much. People like you that help teach others are what this hobby needs. Thanks a ton. Liked and Subbed

[@ChrisHiblerPinball]

I'm happy to have helped!

[@roffels]

This is very helpful, thank you!

[@caprilaser3]

Again Chris, excellent tip! Looks very quick and easy to help find those bad transistors.

[@ChrisHiblerPinball]

Definitely a time saver!

[@ssdobbins]

Very helpful! Thanks!

[@neuropro]

Thank you. Very Helpful

[@carlkoplinmd6776]

I have a flasher circuit that is always on. I determined which transistor controls that circuit, and sure enough, it has a ground fault. Now to repair. Thanks

[@ChrisHiblerPinball]

Glad it helped!

[@itsmekelo5938]

so except for the 4th transistor the energy is going from the red lead directly to the board but on the 4th transistor it has a short and can not go threw the transistor to the board. ?

[@ChrisHiblerPinball]

Yes. That 4th transistor is shorted, and acts like an always closed switch. The test shows continuity between what should be an open switch and the 18V power source.

[@itsmekelo5938]

@@ChrisHiblerPinball Thanks, but I am still confused. It seems to me you should always be getting a beep, even on transistor 4. Or a loop is not being completed and ,,,,,,,, Wait, I am getting more confused. Can you please explain everything from the very beginning? thank you

[@stevenewertt]

will this test also work on Gottlieb systems?

[@ChrisHiblerPinball]

It will, but not quite as nicely. System 80 driver boards separate ground into groups of transistors. You'd have to move your ground probe around. It would work better for System 3 driver boards.

[@rammods]

🤯

[@gquint194]

Do you need to do this while powered down?

[@ChrisHiblerPinball]

Yes sir. And the coil/flasher power and drive connectors should be removed.

[@bigendianian]

Super helpful! Thanks