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twistedsymphony

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I recently took a gamble on an "untested" CPS2 set on eBay. was being sold by a trusted seller so I knew it was genuinely untested.
B-Board works perfectly, it's been tested on other good working A-Boards that I have

the A-Board works EXCEPT the red channel displays full red 100% of the time... so the game looks like this:

cps2_red.jpg



the A-Board still had the security pin in place. so it's never been touched. I don't see any indication of burn marks or leaking caps or anything... PCB looks flawless.

trying to trace back the red pin it looks like it goes through the filter and into 4 sets of resistor arrays, the filter and the resistor arrays seem to check out, from there it goes into a bunch of 74 series logic ICs (is this some kind of Digital to Analog conversion setup?) My initial though is maybe one of the 74 series IC is stuck high but there's a ton of them and the traces are not too easy to follow. and it's difficult to test running because the b-board is in the way.

Anyway, has anyone seen a problem like this before and have any suggestions on where I should be looking to fix it?
 
I have this exact same problem with two AIR BUSTER PCBs.

FWIIW, on one of the boards, I got as far back as the color ram.

Then I got side tracked. Haven't touched 'em since.

Last time I looked at it: CIALIS ( :P ) the Italian tech was telling me to double check my jamma harness connector. Make sure it's not loose.
 
The very first thing I did was clean the jamma edge to make sure I has good connectivity. It's always my first step when troubleshooting boards.
 
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