MCR Video Issue Demolition Derby

Ugries1972

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Hi, this is my first post in this awesome forum. I just ran into a weird issue with my 2p upright Demoliton Derby. I have owned it for 20yrs, been turned off for 10. The 90412 power supply was blowing the fuse, so I replaced as many of the parts from the Bob Roberts rebuild kit as I could. The machine then powered up as the video displays as shown in the photos. The splash screen is great and most everything else is, too. Some of the cars have the weird lines going through them, sometimes they split into 4 parts with the lines. The monitor looks really good aside from that. I have a cap kit, would that help? Any idea what is going on? Is it a monitor thing or a video board thing or??? I would greatly appreciate any help.
Thanks much!
 

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Congrats on your first post!

That sounds like a board thing, not a monitor thing. Want to confirm that? Set a spare monitor up behind your game and run the power / video connections to it. See the same issue there? You know it's a board problem.
Or, back up another game to your game and run the video cable to the other game's monitor and see what you get.

CDJump here repairs MCR games and has godlike knowledge of them so you can always send him your boards for repair. If you do that, send him your linear power board too for him to check out.

Other simple things to try (that probably won't fix the problem but you never know):

1) Test the voltage on a ROM chip and see how close to 5v you are.
2) If you have the MCR board "sandwich" version of the game and are still running the original interconnect cables, ditch them and replace them with the cables that Madrits sells here on KLOV.
3) Spray the interconnect cables with Deoxit and work them on and off the game boards to clean up any oxidation you've got going on.
 
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Thanks for the info. I cleaned the pins the ribbon cables fit on, tested continuity on the ribbon cables, and swapped the cables around. I also noticed a cracked cap on the SSIO board, C139, which I replaced. No change, still garbled video in some areas of the screen, mostly over 1 or more cars. I forgot about testing the 5v, will do that soon.
Any other thoughts/suggestions?
Thanks,
Ulysses
 
Thanks for the info. I cleaned the pins the ribbon cables fit on, tested continuity on the ribbon cables, and swapped the cables around. I also noticed a cracked cap on the SSIO board, C139, which I replaced. No change, still garbled video in some areas of the screen, mostly over 1 or more cars. I forgot about testing the 5v, will do that soon.
Any other thoughts/suggestions?
Thanks,
Ulysses

You swapped the cables around as in took the old ones off and put new ones on from Madrits? The original cables are likely a mess now, 35 years later.

Definitely check the 5V on a ROM chip.

Also check the voltage here:

attachment.php


That picture is from a Spy Hunter boardset; I think you will also have 3 boards in your sandwich and the outer one will look like that.

You might PM CDJump to see if he will post any suggestions for you in this thread. If those don't pan out, you may want to just send him the boards and your power board to check out / repair. He's fast, he does marvelous work, and he's not terribly expensive.
 

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I'd lean toward thinking it's a bad ram chip on the video board, maybe the cpu board.
 
Cables are good, 5v present at various chips and spots in photo. Was around 4.7, bumped it up to 5.1v. Stupid question, but is there an easy way to tell if a rom chip is bad?
 
Cables are good, 5v present at various chips and spots in photo. Was around 4.7, bumped it up to 5.1v. Stupid question, but is there an easy way to tell if a rom chip is bad?

So if it was down to 4.7 at a ROM, that was definitely an issue. Things get really glitchy at that level.

The next thing you need to do (but probably unrelated to the issue you're complaining about) is measure the voltage that the linear power board is producing on the linear power board. You don't want to turn it up so that it's producing 5.5v just to get 4.7v on a ROM because that indicates another problem that needs to be fixed and you're treating a symptom and possibly frying components in the process.

Having a ROM burner will tell you if you have a bad ROM because you can read the ROM and compare it to known good ROMs (like from MAME).
 
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