Whodunnit flasher problems

alexanr1

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I have a Bally Whodunnit and I have been trying to debug a flasher issue. First of all, the machine has a rottendog driver board. So here is a description of the problem.

The flashers for the game are both on the playfield and in the backbox. The flashers are connected through J125 (the backbox) and J126 (the playfield). When a bulb is in both the backbox and the playfield, for some reason they stay on (LIT UP). If I pull out the backbox bulb, the playfield light goes off but flashes properly when fired. I thought that the transistors might be worn out, so I have replace two of them and it has not resolved the issue.

I am about to try to replace Q3 which reads from the bus and triggers the driver transistors, but I am not convinced it is damaged since they work properly when a bulb is in but not when two are in.

Anyone ever experienced anything like this? I am completely stumped!
 
Transitors provide ground, not power. So, I think you have a ground short in the backbox light somewhere. The backbox short is back feeding the ground to the playfield light. That is what I would be looking for. I am not saying it could not be something else, but I suspect a ground short

Just my 2 cents
 
Thanks for the advice. It seemed so odd, so I traced the ground back and it was wired into J105. I looked on the schematic and it showed the ground running to J107. I recently bought this and a Bally Game Show machine from a guy in Cincinnati. Both machines had issued he tried to repair. I re-wired the ground to J107 and everything works now! I guess the moral to the story is don't assume that the previous owner didn't do something stupid like re-wiring the machine improperly!
 
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