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I'm sharing this as a repair log in progress. Of course, if someone has helpful information or ideas, I sure won't turn you away!

tl;dr: I'm trying to fix P1B4 on an IGS PGM motherboard. I found a bodge wire that had come loose and restored the connection (verified with a multimeter), but P1B4 is still not working in the IO test. Tomorrow, I'll follow the trace further to see if I can find another discontinuity.

Longer:
My order of a modded PGM from a community PGM luminary was taking a while, and I needed a way to test some carts I'd ordered, so I ordered a cheapo off AliExpress. Of course, it was exactly what you'd expect-- a mess of corroded-looking traces and black gunk-- but it worked fine except for P1B4. In mediation, AliExpress made the seller refund half of the sale price. The motherboard served its purpose in testing the carts and I still hope to get my modded PGM soon, but since then, I've gotten a soldering iron and learned just enough to be dangerous. If I can fix that P1B4, and there's nothing else obviously wrong, I'll recap the mobo too.

At first glance, I saw scuffed traces all over. The scuffs weren't centered near electrolytic caps or the (empty) battery socket, so I'm not sure how it happened. The solder on the JAMMA pins makes me think something severed the traces and a past owner had to fix it.
First look - top.jpg


The back had more scuffed traces, plus a bunch of gunk around some solder joints. The gunk came off easily with IPA and a toothbrush.
First look - bottom.jpg


After clearing the gunk and looking closely at the back, I found a bodge wire had come loose (red). Sure enough, that through hole leads to the trace on the other side that's connected to JAMMA pin 25 (P1B4). Another bodge (green), tenuous as it looks, is intact.
Bodge failure.jpg


The pad at the hole is torn off, and I couldn't get solder to stick to the exposed trace, so I ended up running a longer bodge wire from the source solder joint all the way through the hole. (Thought it would look better than wrapping the wire around the edge of the board.) I soldered it on the other side to the exposed trace on the front. The shiny flux in the pic makes it look like I bridged the adjoining trace on the front, but my multimeter says they're separate. I verified continuity from the source pin all the way to JAMMA pin 25, so the bodge worked.
Back bodge fix.jpg
Top trace fix.jpg


But when I ran an IO test in Oriental Legend Super Special, it showed it's still not getting P1B4. 😑 Tomorrow, I'll try to follow the trace further and see if I can find another discontinuity.
 
I ended up running a longer bodge wire from the source solder joint all the way through the hole. [...] But when I ran an IO test in Oriental Legend Super Special, it showed it's still not getting P1B4. 😑
I gave the PCB a bath in distilled water, a scrub with baking soda, and a spray on the pins with DeoxIt before noticing... I hadn't enabled B4 over JAMMA on my supergun. 😳 I swear it was a real issue previously! In Martial Masters a few months ago, I was getting P2B4 but not P1B4 on superguns and on my Astro, and that broken bodge was for real, so at least the soldering work was necessary. The clean-up probably wasn't relevant to B4, though the PCB does look much nicer now.

While playing Demon Front, I noticed a couple brief issues:
  • Garbage filled the bottom half of the screen when Twin Horn (under-bridge boss) blew up. The garbage was just bright colorful lines for a frame or two, not recognizable sprites.
  • Voiceover dropped out when announcing Big Claw (crab boss)
I'll do a recap next. I don't expect it will address the above issues, but since all buttons are now working, I want to treat this as a board to take care of.
 
Great work! Sounds like it worked out in the end, and you got some practice time on the bench. ;)

Looks like all the "gunk" is burned flux... definite signs that the board had been worked on in the past. Shame on the seller for trying to pawn that junk off on you.
 
I have repair video and info on my web site and YouTube that may help you
 
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