Did you reseat all of the ribbon cables and not just the one to/from the dmd? I believe there may be one on the cpu to the display driver board too.

Both ribbons are good
Did you reburn all the roms??
I have seen this in person and its seems either a rom issue or the display itself. Swap the display and see what happens

Hey Larry, Ken was able to burn one of the roms you gave me successfully and I replaced it. The other one we cleaned the pins with fine sandpaper and reinstalled. I don't have another large dmd to try to swap it with.

You did verify all the roms are good ?? All 3??? The 2 display and the 1 CPU? You checked all the voltages to the display and the display driver board and they are correct ???
I know there is one line out on his display already.

Verify the 2 video roms are good first
Did you verify all the voltages going to the display are good??

I doubt it will be ROMs. Every chance it is either ribbon cables or the RAM that is associated with the DMD drive.

Just replace the ribbon cables - they are 20 years old and well passed their use by date. They get corrosion inside and you can't see it.

Already changed the ribbons

"He swapped in the other ribbon cable from a Twister he has and no change."

If you mean this it might not be good enough - I would buy a full new set of cables to eliminate them for good.

Ok great
You don't test a crystal oscillator
You test the voltages around it to make sure it has good voltage
If voltages are good then you have a bad crystal oscillator
Time to pull a schematic

Thanks guys. Hopefully we'll get to the bottom of this soon.

Are the RAM chips in a socket on the display board? Try new 62256 RAMs. Looks like it uses two (thats a lot of video ram compared to other systems).

Thanks for posting, Ken. Still looking for an answer to this one. Already have been through the usual suspects, but this is a strange one.

Anyone have any other ideas not mentioned yet? Please let us know. Thanks.

Did you replace the 622256 RAM(s) at least swap the two around if they are in sockets. DE/Sega usually put the large RAM in sockets.

Not to dig up the past here, but I'm having the same issue with my dmd on Maverick . Did you ever get this resolved?

Tried resetting all the ribbons/connectors. Checked voltages back to the big filter cap/BR/fuse in the backbox, and reflow solder on the crystal (X1) and the square IC at U7 as I've read others mention it was an issue in another thread. No change.

barakandl

My controller doesn't have socketed 622256 RAMs so I can't easily switch them to test, and I'm having a hard time tracking the appropriate IC down. I'm seeing two options on Digikey.ca, 55ns and 70ns write cycles. Not sure of the original spec.

Also, I poked around with a logic probe (very amateurishly), and found pin3 on the large 68B45 (U8) to have no signal. Not sure if this is intended or not.