Centipede PCB Issue

LyonsArcade

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Hi Guys!
I'm working on all kinds of stuff tonight, and one thing tha'ts been on the back burner for a while is a Centipede PCB I've got in a Centipede Mini. There's a weird issue with it:

The screen jumps vertically (side to side with the vertical monitor), but only when the board is cold (just been plugged in). If the pcb is in test mode, the screen never jumps. Also I don't get any bad ram beeps when the machine is in test mode. I've tried the board in another centipede cabinet, and it does the same thing in the other cab.

The mini has had the big blue replaced, and all the voltages test out good. I initially started replacing some of the things in the sync circuit, but since it doesn't do it in test mode, I stopped that since I don't think that's the issue. I tested R136, replaced ab10 - 7407, switched P4 (I think this is the sync chip) with another one from a parts board I have... but now I'm looking for something else since it only does it when not in test mode.

I pulled and tested all the roms, everything checks o.k.

Anybody have any ideas on where to look on the board? I'm trying to wade through the schematics right now.
 
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I edited it. It doesn't do it in only 1 part of the screen, it does it when the board is cold. Once it's been plugged in about 10 minutes it doesn't do it anymore, but it still doesn't do it in test mode, period.... and it only does it side to side, does anybody know if the vertical or horizontal object motion circuit does side to side? (I know that's a silly question, but that's the vertical circuit of the monitor, I'm not sure about the board!).

Doesn't do it in test though, making me think it has something to do with the playfield circuitry?
 
It sure sounds like a monitor problem to me. Try this: turn the game OFF, unplug J19 and J20 completely from the main board. Turn game ON. Let sit for 10-20 minutes. The monitor should be on. Turn game OFF, quickly replug J19 and J20 onto the main board, then turn game ON. See if the problem still persists at power up.
 
I've worked on all the contacts but I'll check again. BTW, I've tested the entire cabinet with another board and it worked fine. It may be the edge connector on the actual pcb though, i'll try those contacts (again)
 
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