Arcade Collecting > Pinball
Anyone here have experience in repairing williams pinball machines?
ChadTower:
--- Quote from: pinballjim on August 11, 2009, 03:41:41 pm ---ROMs rarely go bad.
--- End quote ---
They do on Sterns sometimes. I've seen it on Stern vids and pins.
gibbous:
--- Quote from: dansoftcore on August 11, 2009, 10:32:32 pm ---I noticed mine is dropping voltage as well it isn't much just about .4 off.
--- End quote ---
From pin 14 to 13 on U3? According to the schematics it's not supposed to drop any voltage. Goes in on 14 and out on 13 and it should just be a straight through type of deal.
I pulled some of the related chips last night that are also on the R/-W line, but the voltage stayed low. I have a few more to pull tonight. There's nothing but chips on the path, one resistor that shows 5V on either side, so that doesn't seem to be the problem.
I did accidentally short pins 5 and 6 on the CPU (U17) and the diag. display went to zero. Not sure if that's significant or just a coincidence, or even if it's doing any damage, so I didn't do it anymore. :p They are marked VMA and NMI with a bar over the top of the NMI in the schematics.
gibbous:
Turns out the external PS I was using for testing did not have enough amperage to drive all the chips. Had a friend look at it and he hooked up two PSes and got the 7 to turn into a 1. Then found U23 bad, it wasn't passing data on one line, swapped it, and the 1 turned into a 0!!! :applaud: ;D :cheers:
Gonna pick it up and see what happens. :D
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