Hey, this MPU is driving me nuts. I am testing it on the bench, with just the voltages going to J4. When I test it after sitting for a while, the board will flash 3 times. If I reset the power (turn it off and on waiting like 30 secs in between) the led then stays on, however if I jump pins 39 and 40 for U9, it will give me the 3 flashes again.

I've had this MPU for about 10 years, from what I remember I had it in a Cybernaut, and it worked fine (7 flashes etc). I then burned roms for Hot Hand for it, and the LED would stay on. I then realized I had a bad checksum on one of the roms, reburned it, and then I was getting it to 1 or 2 flashes intermittently. I then installed an NVRAM, removed R11, and put zero ohm resistors at CR5 and CR7. Now it does the above.

The board looks nice, there was a small amount of acid damage to it, around the battery sockets, and 1-2 components in the reset section but that was it (just the solder joints look old). The sockets have been replaced (not by me) with machine pinned sockets, and it looks like a decent solder job.

I don't quite understand why when you power cycle it, I get an LED stuck on, then when jumpering it goes through it's 3 flashes. The 6800 U9 looks new, the 6821 U10 looks new. (I can take some pictures of it tomorrow in the sunlight and post them). Is this a capacitor related failure?

There was no trauma to the board at all between when it would get 7 flashes with the cybernaut roms, and when I burned the hot hand roms. What do you guys think of this one?

-Pat

I am using a computer gaming PC power supply. A cheap one I wouldn't use in my personal computer, but figured it'd be overkill for benchtesting mpus. I get 4.97v at pin (40?) on U9 when the led is on, so it seems like the board is getting good voltage?

Please see pics attached. If anyone needs any other sorts of pics, please let me know. I'm handy with paint.net, and have a decent phone for hi-res pictures. It looks like it's going to rain a little more here, but I can get them throughout the day. I'll go out and remove U10, take a picture of the socket, and try to get a side view of it as much as possible.Top -35 (resized).jpg

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One thing I should note is, I changed out the LED to a super bright LED. https://www.amazon.com/dp/B0779RK247

I spent a lot of time and research on getting these, but still aren't 100% sure they are the right spec. I wasn't sure if it was possible to bring down the 12v that much to cause an issue when it's powering the led.

More pics. This is of the U10 socket, J4 connector, a little more of the reset section, and my test bench setup.

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You mean for ROMs? I have it jumpered for 2732s, which was what Cybernaut was.

Edit: LOL I still haven't answered your question, I intend to use it in Hot Hand.

It's amazing. I've never done board work in which I've taken pictures and looked at bad solder joints that way.

Pin 33 on U10 was not making continuity down to the VIA to U11 pin 33.

However, when repairing that trace, and turning on the test bench, I just get a solid LED. But when I short pins 39&40 of U9 I get 6 flashes. So, I guess I'm going to try the board in the game, with just J4 connected and see what happens.

-Pat

Yes, that is the trace I repaired. I guess I need to invest in some sort of magnifier or microscope. It still looks "ok" to me, but obviously it wasn't after testing. Got rid of the wire also.

Are you saying those components could be the cause of the locked on led on the bench? R113, R16, and R21?

-Pat

Okay, now I understand where I am confused, if that makes sense.

I did not know Cybernaut used a -133 Bally MPU. I thought it used a regular -35 board. The mod you are suggesting by putting the diode back into Cybernaut at R113 would convert the board back to a -133. I was familiar with Baby Pacman and Granny and the Gators (I think) using the -133 but not Cybernaut?

(By the way, this Cybernaut I had, did have one of the 6802 prototype mpus in it that I sold with the game, which was why I wanted to put a -35 in it.)

-Pat

Thank you for the clarification. The R113 and R16 upgrade to 1/2 watt is good to know.

This thread is resolved, and my other sound card thread is resolved also. Done! I will replace those resistors with the upgraded 1/2w and not worry about the board for a while.

-Pat

So kind of an interesting find.

For this MPU in this thread, it's working perfectly now. I started working on another MPU with acid damage to see if I can fix it. Spent the last few hours on it, and needed to start testing chips.

When removing the EBD roms I burned (2732), and placing them in the known good board, the power supply didn't have the issue where the led was stuck on. It booted up immediately. Tried it 3-4 times, and same thing. Put the Hot Hand ROMs back in the known good board, and voila, same problem as before led stuck on. Yes it booted up if I shorted the reset but strange behavior I thought.

Then, I started testing all the chips one by one in the known good board (on my 2nd board, it was the CPU that was the problem). When I got to the U11 PIA, I put it in the known good board, and whammo, booted up again perfectly. I tried it 3-4 times and same thing. I put the original known good PIA back in the known good board, and voila, again. Led stuck on, but will reset when shorting pins 39&40 of the cpu.

I thought that was so neat that when swapping eproms, and a different pia in U11, it fixed the problem on the bench. At least I have a good mpu now for Hot Hand, and a 2nd working one that I can use as a testing board.

I'm just absolutely fascinated with these MPUs now that I have a little more confidence in soldering skills, troubleshooting.

-Pat

I have not specifically overwritten these roms, however, I have taken your advice on several other eproms that I have burned, and this works great. Slowing down the programmer all the way and writing them the first time at least twice, seems to resolve a lot of the weird funky issues I was getting with burning eproms.

Thank you Quench for the suggestion, this is one of those things that I will be doing all the time in the future.