DMD issue, where to start looking?

[BMHouze]

Seems my Checkpoint is having a weird DMD issue.
I usually play 3 players and have been having some sporadic issues with the DMD. Sometimes it works just fine. Other times it will only show the player 1 and 3 scores, sometimes it will go blank during the player 2 play just to work again on player 3, and once it went all weird and had a broken single line on the the display for the rest of the entire game.
I am pretty sure it's not an issue with the DMD as it is displaying just fine, I feel it's an input issue. My tech guy thinks it's a delay timing issue.
It would be nice to have a few ideas where to look when I have him come by with his logic probe.
Thanks for the input,
Brad

 

[Menace]

I'm going to assume that Checkpoint dmds are handled the same as all DE Dmds, in which case the DMD has its own mpu separate from the game mpu. DMD images are "called" from the main, and what you are experiencing is likely due to bad or interrupted calls.

I would start with the easy stuff and reseat the ribbon connectors at the mpu and the DMD, might as well do all the connectors on the DMD controller pcb and see if that makes any difference.

From there, check to make sure your game has the latest game and dmd roms.

If that doesn't pan out, I think there was a TSB regarding the ground and 5v supply connector for the dmd controller, so Google that and see if that has been done, and if not do it and go from there.

Hope this helps.

D

 

[BMHouze]

When I originally picked the machine up it has DMD problems that were easy to fix a blown capacitor (I believe) my tech guy didn't have the right one at the time so we cabbaged together a few to get up to the required voltage. I am thinking of starting there first (as I have the right parts now but didn't swap it out cuz it seemed to be working just fine) and then my tech guy is thinking it may be the display strobe decoder (I got my manual back form him) on the CPU board as the next place to look.
thanks,
Brad

 

[Menace]

Don't over think it... and always remember K.I.S.S. Start with the easy stuff first and work your way up from there. DE DMD's are notorious for having communication issues like this, it's just a nature of the design.

D