+5v JAMMA pin burned out on switcher

alfonzotan

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Had a weird failure in my Multi-Williams over the weekend. I'd had a BitKit2 in the second slot of the JAMMA switcher that usually alternates between a JROK and a Moon Patrol stack (with a JAMMA adapter). Decided I wanted Moon Patrol back, so I pulled the BitKit and plugged the stack back in. The game started up with no issues, but didn't have sound. After I checked the connections and powered back up, I got some smoke and a burning smell, so I immediately killed power.

Check of the power outputs from the PSU (Happ 200W Power Pro, new one) were all nominal. When I looked at the main JAMMA connector, Pin 4 was burnt at the harness connection to the switcher, and the finger on the switcher was fried:

IMG_5856.jpg

The two wire inserts there are for +12v (Moon Patrol audio amp) and sync. They've both been in for a couple of years with no issues.

Really have no idea what exactly happened here. Something got bumped and made a short would be my best (and probably incorrect) guess. Have not tried to test either game board yet, but at least there's no visible damage.

Any thoughts/suggestions? I'm inclined to move the +5v wire on the harness (custom job for this build) over to Pin 3 and start testing carefully from there... I have a crap 60-in-1 board that can be a guinea pig. I've cleaned all the fingers on the switcher since this picture was taken, but nothing further.
 
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I'm only speculating from your photo, but It looks like maybe your Jamma harness was only using one out of the four available +5V pins. If that single pin connection on your harness was weak/loose, it likely would have heated up and caused the scorching that you show in your picture. Especially with a game that pulls a lot of current from the 5V source.
 
I'm only speculating from your photo, but It looks like maybe your Jamma harness was only using one out of the four available +5V pins. If that single pin connection on your harness was weak/loose, it likely would have heated up and caused the scorching that you show in your picture. Especially with a game that pulls a lot of current from the 5V source.

I took apart the harness cover, and that is exactly the case: +5v is only connected at a now-scorched Pin 4. Would be easy to run additional 5v lines from the PSU to the remaining pins (and replace the bad one).
 
That was an excellent observation and suggestion from @RiddledTV... turns out the custom wiring harness I'd had made for this Frankenstein had one measley 5v wire, and it wasn't even 18ga. I went back in and added new wires for all four 5v pins (benefits of a beefy PSU), and replaced the burned out end connector finger with copper tape and Goof Off (now I can't find the thread where I picked up the repair method, but it worked great):



IMG_5863.jpg

Cleaned up the switcher, rewired everything, and now I'm back to functional. Better than back, actually: as there's now enough current making it through for all the boards, I was able to back the 5v voltage all the way down from 5.6v to 5.1, so everything should be much happier now (Moon Patrol would glitch with the input voltage lower than that in the previous configuration).
 
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