So, I have a System 6 MPU. It will boot to audits with both LEDs flashing then going out. However when I press the advance button on the coin door to go through audits, the displays go blank and nothing else happens. Board has new connectors and new 40 pin interconnect.

Anything come to mind to any of you pros out there?

For reference, I'm testing this MPU in known working Gorgar Pin, including the driver board that has a new 40 pin. I pulled my working MPU out and put this one in to test.

Thanks for any advice.

Any thoughts from anyone?

Ok, thanks for the reply.

I did the diagnostic test you posted and only the bottom light comes on so I'm verifying the RAM socket and traces now. I'll report back what I find. I'm aware of this test, but for some reason I had a brain fart and figured it made it to audit mode (showing game number/version etc), RAM must be good...

Test/Audit mode - With coin door open, in audit, with manual down, pressing advance should make the displays go blank, then pressing advance once more and changing to auto up would walk through tests (displays, solenoids etc.).

For this MPU, either in manual down or auto up, there is no return from the blank displays.

Thanks I'll report back soon.

Ok, checked socket, all pins check out. Tried several RAM chips, including one from a different working board. Working board functions perfectly with questionable MPU ram installed as well from non working MPU... I'll keep digging.

OMG, I have to work on my reading comprehension late at night. I did say brain fart!!

I am using IC14, IC17, and IC20. Those are all original RN sockets and are clean and in good shape. Tested with known good ROMS from a different working board.

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Ok, after looking very closely at my own photo so see a trace that appears to have taken a hit and it only connected by a thread between pin 1 and 2, leading to pin 23 on IC20. Continuity is not reliable. I'll repair this and report back.

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Well that was it. Bad trace. Thanks for sticking with me while I got my head out of my butt and started thinking straight! Working! Haven't given it the full long term testing yet but just played a couple quick games on Gorgar with it.

Thanks!