(Topic ID: 131622)

Williams System 9 Stuck Coil (Comet)

By BlobfishXL

8 years ago



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#1 8 years ago

Ok so I had a catastrophic Transistor failure (there was a lot of smoke).

The Diode for one of the pop bumpers broke off and the coil melted which lead to it's transistor melting as well.

Fixed diode coil and the big and little transistors associated with that coil.

Some second order problems have appeared: None of the special solenoids will fire and the left sling is stuck on at power on. Also the relay that makes the solenoids work during play is chittering, but eventually engages. The flippers work when the relay is done chittering. Further none of the flash lamps work.

Should I replace just the transistor for the sling? Does one stuck coil transistor make all the other ones not work? It looks like the flash lamps are somehow special solenoids too...

#3 8 years ago

I have a logic probe.

I pulled the board and the same transistor that blew before is shorted again. Probably cus I didn't notice the coil had melted at first, so I'll start with that. Is it the case that a messed up transistor can mess with other coils?

#4 8 years ago

Ok new transistor in. I don't know how to test the 7402's, but the burnt transistor leads to U6. With no power, U6 seems to have some pins that short to ground whereas U7 has none. Don't know if that is proper.

2 weeks later
#5 8 years ago

U6 was the culprit. It tested with a pin shorted to ground other than the ground pin. Replaced it. The original transistor that had blown had blown a second time so had to replace that too. It had blown the second time cus the diode was oriented backwards on the new coil and I hadn't checked. So new diode new tip122 and new 7402 and I was back in business.

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