I've got a Bally -35 MPU board I'm trying to repair and use in my Black Pyramid. Based on the jumper settings, the board appears to be wired correctly for a 2532 at U2 and U6 based on http://www.actionpinball.com/tech/35_rom_mod.php

However, what I see is a 2532 in U2 and windowsless "8212" chip in the U6 slot that contains a printed U6 and bally 1981 copyright. What is this chip? I have no idea what board this came from. Is this chip reusable or do I need to get another 2532 to get this board functional in this game.

Yes it's exactly that chip (and socketed). So, sweet?! So all I need to do is re-burn U2 and, assuming the rest of the board is sound, I should have a booting game?

It's completely untested. The game came missing an MPU so the seller sent me an untested spare. The U2 EPROM has a Bally copyright date of 1982 so I know it's not from BP since that was produced 2 years later. Was just going to erase it and burn the ROM I've got. R11 is cooked and I was going to put NVRAM on it. I just wanted to make sure I had good game ROMs before I attempted anything else.

My question was whether that U6 chip was game-specific?

To Followup, I burned U2 successfully over the existing EPROM. Cut out R11, CR5/CR7 and jumpered them and installed NVRAM at the 5101.

I've now got a game that is SUPER close to booting. I get an attempt at attract mode with a second or so of light sequencing on the PF and backbox, which repeats indefinitely. LED is solid on. Voltages test good on the reset line, hail line, VMA line, suggesting I'd got a data/bus problem somewhere. Not surprised. There was some minor corrosion at the bottom of the MPU which I have resolved and replaced a few nearby components and tested continuity.

I don't have an AID2 module like the Bally Repair Manual suggests. I do have a logic probe. Has anyone got Leon's test rom to function in a board that has a 2532 at U2 and the E720-53 PROM at U6???

Isn't U12 a display control timer? Regardless, I do not have an oscilloscope.

Pin 39 of U11 is stuck hi.

What I did notice is that U9 pin 5 is erratic, given reading solid readings that vary between 2 and 4.5V at power on and/or hitting the test switch. Thinking the U9 6800 chip is bad? Will have to wait on a replacement.

U11, pin 39 is stuck hi. Pin 40 starts lo and then pulses.
U9, pin 39 is lo, pin 40 is high.

I'll post the other readings shortly. Corrosion was pretty minimal. I suppose I should remove the U11 socket to see as that is close to the battery. There was nothing around U12 at all. Nice and shiny. I do have strong pulse readings on all the address and data bus lines.

The other abnormality I noticed is at the bottom of the board by the battery. The top part of CR44 measured 0V, but the button part (and TP6 measure just under 1V which seems like an unusual state). The schematics aren't clear as to what TP6 should read.

FWIW, this is now on the bench, 5V is 5.04, gnd and 12V also applied.

Please re-check my post above. I had U9/U11 crossed up.

Anyways, I removed and replaced the DIPs for U8 and U11 as there was some corrosion underneath.
My multimeter does have a Hz setting, but I got 0.000 at both pins above.

Now I have a new behavior and power up. The LED light briefly flickers (after which TP6 reads ~11V) ). This behavior seems to remain consistent through pressing the test button, but occasionally will light solid.

I pulled U10 and U11 and while U10 is clearly labeled 6821 with a manufacturer on top, U11 had no discernable marking on top and was labeled 3921X underneath.

I think I'm going to test this back in the machine, as the flicker should be good??

I guess the flicker is a positive sign, but nothing but GI when plugged into the board. When I apply power, I either get a bunch of stuck hi/lo address pins, or they pulse correctly. I'm not convinced at all that the reset circuit is behaving correctly.

I have pinned out all of the U6/7/8/9/10/11 circuitry and it's perfect. Everything buzzes out where it should and no crossed up signals.

To accommodate the NVRAM at U8, I took barakandi's advice from another thread, removing R11 and replacing CR5 and CR7 with 0 ohm resistors (jumpers).

My next step is going to be to replace Q1 and Q5 although they are not in the corroded area. Q2 was, and was replaced along with the LED before I did any other work.

Yes I have a logic probe and have been using it extensively. I feel like I have a solid understanding of the circuitry at this point.

The reset circuit works fine when shorting U39/40. Wasn't aware that a switching PS would factor into that. NVRAM tests fine (5V/0 ohms resistor to TP5)

All sockets have been replaced. All pins verified with continuity. Nothing shorted and no traces cut. I've got a verified 2532 EPROM in U2, the 9332 in U6, a chip in U7, NVRAM in U8, 6800 in U9, 6821 in U10 and that unknown "3921x" chip in U11.

I noticed that line A7 is not pulsing with the same frequency as the others. It sounds "weird". I also noticed that the R/W line upon reset pulses 2 or 3 times, then locks on high.

So since I'm not getting any flashes after the flicker, I assume the ROM check is bad. This board was NOT from Black Pyramid (per original post). I erased/burned/verified the U2 ROM onto the 2532 from http://www.ipdb.org/search.pl?any=black+pyramid&search=Search+Database&searchtype=quick
the filename says BLKP2732.U2. Should it not make a difference that I have a 2532 chip?

But the U6 chip does not have a window to erase it (see original post). Do I need to do anything there?

Alright, NOW we're getting somewhere!

Sure enough, at U9 found with a magnifying glass that one of the "in between" traces had lifted and was touching the A7 signal. Repaired that, tested with just U9 present. All good address signals. Put back in U6 and U11, good.

Then we take an interlude where I'm a dumbass and start inserting the remainder of the chips while I had power applied.
Screwed up the U2 EPROM, but thankfully it erased and reburned without issue.

NOW I get solid 3 flashes. Which means U10 is screwed up. Not surprised since that's the one with no label and may not even be a 6821 chip. Hoping to borrow one from a friend...but have some on order with Jameco.

It lives!! Found u10 pin9 (an in between trace) connected to u10 pin31, which caused a bizarre signal on PA7. Literally a speck of solder under the DIP I added... took a high powered magnifier to find. Game boots for the first time and I have good displays and solenoids!

Thanks for your help. Now onto cleaning up and shopping this mess