Cheetah
Stern Electronics, 1980I just picked up my first early solid state, Cheetah, and I'm having a problem with a couple of insert lamps. At first I thought they were bad bulbs, but that wasn't the issue. When I bypass the lamp holder with a good one they still won't light up. After checking with a multimeter, neither are receiving power. I can trace the wires up to the lamp board, but don't know where to go next. Any suggestions? Many thanks in advance.
How did you check with the multimeter? They should all have 6V via the bus. It's hard to measure the other (ground) side that goes to the board well due to the way they're pulsed.
Usually though, in this case it's the transistor for that light on the lamp board that's the issue, or a bad solder joint on the connector.
The lamps are powered by the bare braid stapled to the playfield, so unless the solder joint broke, you have power since the other lamps work. You can verify with a multimeter using the ground braid in the cabinet and testing for voltage at either wire on the socket.
zacaj is right, you probably have a bad SCR on the lamp driver board.
I forgot to mention that one of these lights originally did work and then stopped. I'll try replacing the SCRs for those lamps on the driver board and see what happens. I admit that I don't really know what I'm doing with the multimeter, but the other lamps were pulsing when tested and both of these bad lamps were just sitting around 0V.
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Rochester, NY
Vaudreuil-dorion, QC