I have used other monitors that have worked fine with other games. This is at least the 3rd monitor that I have tried, and all of them have the same scrambled picture on them.
The game seems to play fine otherwise. I can coin up and play the game, and all the sounds work. The picture is the only real issue at this point. I couldnt get a pic of the monitor chassis or the make or model, but it is out of a Pole Position if that helps.
One other thing i noticed: it seems there is a part missing from one of the boards. I'm not sure it is causing the screen issue, but i figured id mention it (in pics below).
I agree with the assessment that this looks like a sync issue. It's good that the board seems to fully work other than this problem.
There are a few possibilties to consider:
0) a sync problem with the monitor. Seems extremely unlikely, as you've tried several known-working monitors.
1) (no offense intended, but perhaps) you are incorrectly connecting the monitor. The game PCB outputs a composite sync, which is both vertical and horizontal sync combined onto a single wire. Some monitors need this hooked up slightly differently. Often, a single (composite) sync wire goes to the monitor, and it is "looped" to connect to both the H & V sync inputs of the monitor. As Bob describes, the K7000 is a little different; composite sync should be connected ONLY to the H input on that monitor. Read up here:
http://arcadecontrols.com/BBBB/sync.html
2) A connector/wiring problem between your PCB and the monitor. Find the video output on the PCB; check the edge connectors (both the PCB fingers, and the pins inside the connector). Check the other end. Check continuity from one end to the other on each pin. Check the connectors/pins on the other end (that connects to the monitor) too.
3) A PCB problem. These come in a few sub-varieties:
3a) physical damage; a scratch or gouge or something else has broken a the trace with the sync signal on it. If it suddenly stopped working, without possible cause of such damage, this is unlikely. But if someone was working inside the cabinet, or doing anything which could have caused damage... look carefully for it.
3b) the 74LS125 @ IC91 on the video (bottom) PCB. This buffers the sync signal just before it leaves the PCB.
3c) We really hope you've found the problem before here. Because almost the only other thing it could be (IMHO) is the large custom IC 106. It generates the sync signal. However, it's likely almost impossible to find, and expensive/difficult to replace. If the problem isn't fixed before (3b), it's pretty much a lost cause.