Hey folks... I'm having a hell of a time with my Black Jack. It boots and plays, but after being on for 10 mins it will randomly add credits and points during a game and random controlled lights will get stuck on. Then after a while longer, it will just reset over and over with either 3 flashes then nothing, or one or two flashes with the LED stuck on, sometimes no flashes at all and no LED, sometimes the LED is stuck on as soon as power is on... etc etc.

If I leave it off for a while, it works again but the cycle repeats... it happens both on the bench and in the game. Boots fine at first, then it goes screwy after it's on a few mins.

There's no corrosion on the board at all, it's very clean, but I've rebuilt the reset section anyways. I've replaced the U6, U7, U8, U9, U10, U11 IC sockets. I removed the RAM/battery and added barakandl's NVRAM. I replaced U11 and U10 (with new 65C21). I replaced U14 (with new CD4049UBE). Nothing's changed. I have +5v everywhere that needs it, and pretty sure there's pulses where there should be but I just get lost after a while of checking.

Since the board starts up and plays fine after it's been off for a while, I'm thinking it's a bad IC... something heating up internally and failing. I think have every part on hand to replace everything on the board (except a 6800 and a 6810 unfortunately... and those are the only 2 IC's getting slightly warm).

I dunno where to go from here. Could someone give me an idea what to check to confirm which IC is bad? ...or any other ideas? Thanks!

I've replaced the U6, U7, U8, U9, U10, U11 IC sockets. I replaced U11 and U10 (with new 65C21). I replaced U14 (with new CD4049UBE).

I haven't replaced any other IC's yet, I was hoping for some things to check out to confirm where to go next, rather than shotgunning them all... though I do have some 4011's maybe that's worth doing next. Mine is doing the same both on the bench and in the game though.

Hrmm... OK. Thank you.

For what it's worth though, I did some research on this before I bought them. I read posts from GPE and barakandl on here and other message boards that say this part works as a replacement (NMOS)... so I was going on that info. Here's the exact part for reference: https://www.mouser.ca/ProductDetail/?qs=opBjA1TV902p0LqHsLVgSw%3D%3D

Anyway... the boards behavior didn't change when I put these in, so I guess it rules U10 and U11 out as an issue anyways. I can put my original 6820's back in but the problem still exists with those.