OK - the title says it all. I am asking those who have experience in such things as to what else I should replace besides all of the chips. I am assuming that every chip is blown, including NVRAM, PIA's, game ROMs, etc.
The board itself is free from battery damage, so that's why I want to repair it. Is it safe to assume that I blew every chip? What else should I plan on replacing besides all the chips?
For the curious, I did this while bench testing the board - it was not in the machine.
Why would you really want to do that?...practice soldering skills? Even if you didn't blow all the IC's (current takes the path of least resistance - so it is possible that something went first). Anything on the +5V buss may be stressed. There's around a half dozen tested working boards on Ebay for about $100-$125. How much is it going to cost in parts if you don't troubleshoot it and just dive in and replace everything, not to mention the time?
this happened to me once by accident. it indeed blew every chip on the MPU board, and i think (it's been many years) i think the 4543 chip on some of the score displays. i think the SDB and LDB survived (though i'm not sure why.) Sound board no problem because it uses 6 volt AC GI power for it's buss.
Depends. If you are lucky something hard shorts fast and blows the fuse. 43v has a 5a fuse tho.
I had it happen to a new replacement MPU. 43v is one pin away from 5v on the j4 plug. Connector with no key gets plugged in one position off sending 43v to the MPU. The 27128, 6802, and NVRAM was dead. Everything else survived.
When people send 12v down the 5v rail on the MPU U15 tends to go short and blow the fuse and a lot of times that is the only failure. Sometimes u15 will literally explode.
The 45 volts was from a battery, and yes, I hit the 5 volt pin on J4, got a nice arc from my clip lead to that pin. I doubt if I am lucky enough to only have one component go, so I am going to go the shotgun approach.
Right now, the board doesn't even get the 5 volt flash on power up.
Sounds like general consensus is chips only are damaged/destroyed, the other components are ok.
Thanks
Quoted from Billc479:The 45 volts was from a battery, and yes, I hit the 5 volt pin on J4, got a nice arc from my clip lead to that pin. I doubt if I am lucky enough to only have one component go, so I am going to go the shotgun approach.
Right now, the board doesn't even get the 5 volt flash on power up.
Sounds like general consensus is chips only are damaged/destroyed, the other components are ok.
Thanks
the 4000 series chips are less likely to be bad than the 7400. After an overvoltage situation, bad chips are likely top get really hot or even have a direct 5v to ground short. So check for hot chips.
What I would do is to swap the socketed chips into a known good CPU. Once you weeded out bad socketed chips and if it is still locked, I would do U15 (fails often on overvoltage) then I would run the board with just the CPU installed and check that the reset works, both clock phases active, CPU is running, VUA-Q2 is active. Next up logic probe out the U6 socket stuff like /A11 at P20 and /CE at P18 must be pulsing. U11 has to work too. The PIA CS is A9+A12 coming from gates at U18 and U17, if either those dead, the CPU will be locked.
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