I went off topic and mentioned this in another thread, so I thought I would make a thread in case someone knows the solution or runs into the same problem.

I just got my Mr and Mrs Pacman up and working with a lot of help! I probably would have never made it this far completely on my own...Actually? I know I wouldn't have!

One of the problems I was trying to sort out today was that I didn't have any GI lights, And the red part of the pac maze was confused. The red lights weren't spelling out anything, and were just doing what they wanted. Still fairly new to all of this I'm studying the schematic and trying to check anything I could think of. Convinced U1 on the Aux Lamp Driver board was bad. But I wanted to be sure ,so I started playing around with the logic probe.

I touched U1 pin 2 with the probe and everything started working! The GI lights came on, and all the red pac lights were working like they should! Take the probe off and everything goes back to the way it was! What the heck is going on? I check wires, check connectors back to the mpu. Can't find anything yet.

After a while, I went back to the Aux Lamp Driver Board and decided to stick the DMM on pin 2 of U1 to see exactly what is happening when I touch the logic probe to it. Without the probe, It reads 5.1v, with the probe it reads 5v even. The probe was pulling just enough to make a difference.

So, I'm guessing if the board was at exactly 5v. everything would work like it should? But since it's 5.1v. It's just enough to make that whole row U2 through U5 off enough not to work? Huh?

As a temporary fix, I tied the line that u1 pin 2 is operating to all the other chips to 4.97v with a resistor to ground and everything is working great!! If I try to hold it down too far it trips the under the play field relay and throws everything out of whack again. But at 4.97v everything works fine.

I don't know enough to know what the actual problem is, I just found the temp. solution. Maybe I still have an issue back at the mpu. I'll look further into it tomorrow.

Are these things that touchy on voltage? or do I have a deeper problem? Or just a bad U1? U1 is working great at that little of a drop. Crazy! That's not even a half a volt difference!! 0.1v is the difference between whether it works or not!

In lamp test, I have no GI's, Or maybe I'm calling them the wrong name? The above play field lighting. The red in the pac maze was all mixed up. not really following any pattern. And a couple under the play field lights weren't working.

My Mpu, had real bad battery damage, I had everything off of the board, new everything, with exception of two caps, and u7, because I ordered the wrong parts.

New pins on mpu, and aux light driver board.
I started with the schematics and traced everything to the Aux lamp driver board.

I've been going over and over this in my mind trying to sort out the possible problem, and why the "hack" works. Maybe a weak signal on the mpu? That would be the AD1? or lampstrobe? I think, I didn't write it down. Somewhere in there.

After dropping the voltage, just that little bit? I have not had one problem and everything works like it should! Weak signal? or bad U1? on or to the aux light driver?

I'm getting what looks like a regular pulse from the mpu, it looks like the other lines.

Just kind of weird that dropping that line on the aux light driver on the output of U1 by. 0.1v makes it work, and puts u2-u5 working like they should! Today, I'll backtrack to the mpu and recheck traces as a start maybe the input to U1 is weak. I might have a weak trace, I've fixed about 8 or more of them so far trying to make this mpu solid. I thought I had them all, but I'm sure I could have missed one.

I might be wrong, but the Gi's are controlled through the aux light driver board on this game. What I'm having an issue with are most of the lights or a good portion of them that are controlled by U1 through U5 on the aux,Light board.

I have it narrowed down to this but not really sure , and I'm still new so I could be way off, that and my writing sucks!

It's what ever is controlling U1, or U1. somewhere along those lines. Then from there, U1 goes out and controls U2-U5. I'm still new to all of this so I'm sure there could be another issue somewhere. But that's where I keep ending up. I've traced the signal the whole way back to U10 on the mpu. Pin 2? I didn't write it down, also a pin on U11. and U20 pin 3....the voltage is a little low at 1.7 v .... But consistant the whole way to the aux light....

If I unplug the aux. light board? I will completely lose all the lights that are mentioned. The red pac maze, the above playfield lights, the relay that flashes the above playfield lights, and a few others. That board is what controls all of those. All of the mpu controlled lights or lights that work from the lamp driver board are fine! So, it's specific to U1 on the aux lamp driver board....I think? HAHA....

Until I have another U1 in my hand I won't know for sure, I was just trying to play around and make sure that was the actual problem. With one of the outputs from U1 tied down a fraction of a volt, it's allowing all the lighting to work perfect...For some reason..

I'm still poking around and looking...Trying different things....

That test Rom would be cool to have through all of this! That would have narrowed some things down!