Hey guys. Trying to wrap my head around a Bally Space Invaders that we had set on 1 credit / 2 coins. At some point it began to give 1 credit / 1 coin without any changes to the dip switches. Initially, I thought the dips may be bad, as I had confirmed all of the dip switch settings were correct. I actually tried to jumper the dip connection on the backside of the MPU and it still wouldn't give the proper credits. I still thought maybe it was dip related so I ordered some replacements, however, I never installed them because the MPU failed and would no longer boot approximately 1 month after the initial problem.

We installed another -35 MPU and oddly enough, the same issue still exists. I've changed the dips to different settings and there will be variations in how many credits one coin will give, however, it is never accurate. I would be highly unusual for both MPUs to have similar dip switch issues. It is leading me to believe there are some wiring issues that have presented themselves. Switch matrix problem? Any thoughts? This is a genuinely strange issue.

Oh yes, we ran it at .50 for months and then it decided it wanted to be set for .25. One of the strangest issues I have run across on a pin. We haven't changed or modified the game code or replaced any of the roms at U1, U2, or U6. I could try to burn a new set to see if that fixes the issue?

Not the best pics but is what I had available.

I will have to go get some better pics. Thanks.

We’ve looked at all the coin slots. It isn’t related.

I finally got around to taking a picture.

20210901_123728 (resized).jpg

I actually found an older thread with the same issues, however, the links are dead. Where can I find the rom for the U6

I have a mystic u6. Would I need to move jumpers around? I think they are different chips, so very likely. Does it matter if the code is written on 2 or 3 roms? For example if I download the code for a u2 / u6 rom arrangement, but put in the mystic at u6, will it work?

If I download the SI u2/u6 code and burn the u2 to a 2716, the leave the Mystic code u6 I should code. I'll have to jumper the mpu for 2 roms and 2716s. Thanks Quench. Keep you posted.

Actually I am using the Mystic board in SI. It had 3 2716s but I moved the jumpers when my SI board died. I no longer have the Mystic but I have the mpu.

Cause it has been jumpered to 9316

Quench I have not got around to burning a 720-35 U6. Anywhere I could order a set from? Any chance to get a 9316 U6 -35 so I don't have to rejumper the board?

Ordered. I'm actually trying to sell it but it looks like it may stay in the collection.