Future Spa
Bally, 1979Working on Future Spa. Stupid me. I did the upgrades to the SDB, new electrolytics, ground mods, and tied TP1 and TP3 together. Well, actually I tied TP1 and TP5 at first and blew the 5V-4A fuse on the power supply. Then I found the jumper I had installed wrong. So I fixed the jumper, now TP1 and TP3 are tied together, but when I power up, I get a solid LED on the MPU board. No flashes or flickers, just solid. The voltages on the TPs are reading in range. What have I ruined?
So, you sent 12v into the 5v chips of every board in your game?
I'd suggest you swap all the socketed chips on the mpu with ones from a known good board. If it still doesn't start flashing, I'd either shotgun replace all the other chips or just junk it.
Good chance you damaged some other boards too
Put your finger on each chip, if any feel HOT they're fried.
The 4000 series CMOS logic chips at U20, U19, U18 and U14 are rated to 18V max power so should have survived. The other chips will be in question.
Removed all the socketed chips from the over voltaged board (see picture) and put them in a known good board and installed in Future Spa. All works correctly so I have concluded all the other boards in Future Spa are good. All the removed chips are good. So the issue is with the pictured board that saw the over voltaged 5v circuits. Can someone suggest where or how to test further the remaining components?
Quoted from JethroP:Should I put all the socketed chips back in before check u15 u16?
You don't need the socketed chips installed to check the clock circuit of U15/U16. The clock pins should be oscillating if they're still working.
Quoted from JethroP:Well, it's been powered down for an hour so everything is cold.
Sorry, I meant to touch the chips with the board powered on for a few minutes.
I have sen U15 eat the short a few times and protect most the rest of the MPU on a 12v to 5v oops. Sometimes U15 literally explodes when this happens.
EPROMs are another device likely damaged too.
On my logic probe, the pulse light turns solid when checking 8 and 11 on U15. Checking my other game that has booted up properly, my probe reacts the same...solid pulse light on pins 8 and 11.
Quoted from JethroP:On my logic probe, the pulse light turns solid when checking 8 and 11 on U15. Checking my other game that has booted up properly, my probe reacts the same...solid pulse light on pins 8 and 11.
Its going to be hard for anyone to know at this point.
EPROMs and U15 are most likely suspects to go on a 12v short to 5v. Then the U8 RAM, then the U9 CPU. Sometimes one device goes short, the fuse blows, and protects everything else. If the 12v festers for a while before something goes low resistance and blows the fuse a lot could be bad. Usually in Bally world, its not to bad... but... could be.
Try the chips one at a time in the working board. U9, U10, U11, U8. U7.
If the boards are strapped for the same ROM type swap those too.
I took all the socketed chips from the over voltaged board and installed in another MPU board. That board boots fine.
Clarification: Checking U15 pins 8 and 11 the pulse light was on on both boards I tested, but on the bad board the green "level" light was on at the same time, whereas on the good board the "level" light was off.
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Rochester, NY