1
Apr
'13

No, not the one we live in, but my pinball machine.

The upchucker and the 5-bank reset were not working, and the replacements have been sitting around for a while, waiting for a rainy day. Well, today was that day.

Replaced the upchucker coil with an A-4895 as per Clay’s notes* (the manual calls for an A-5194) and the fuse with a 2.5A slow-blow (again, Clay’s recommendation) and it worked about three times before the relay arc’ed and the fuse popped. I might need the pop bumper driver board modification, but I’ve been thinking about it and I don’t think it’s necessary.

SW31 tells the CPU that there’s a ball to be up-kicked, and the CPU then pulses the K relay once which kicks the ball… once. This is what the pop bumper driver board also does, except using a one-shot (74121 originally, 4538 in the Rottendog replacement) and not a CPU (well, except for the www.homepin.com solution, which uses a PIC).

My problem is that the K relay is failing, and replacing that with a modern transistor should do the job. This seems to be what’s happening here, as far as I can tell that’s a PNP/NPN pair driving the coil, the capacitor provides extra oomph locally, with the oomph held locally by the big-arse diode. It might be a hack, but I think it’s a good hack.

I also replaced the 5-bank reset solenoid, no joy. Clay (again) notes that the transistor is very likely to fail, so I replaced it with an MJ2955 I had kicking around and all is well.

Under playfield transistor on right hand side of lower playfield — this transistor is driven by a lamp (low current) output and drives the 5-bank reset coil.

* Which I downloaded way back before he went commercial. Seems one has to pay for them these days. I would. They’re really good.



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