UMK3 PCB Repair Log

zenomorp

Well-known member

Donor 2015
Joined
Apr 5, 2008
Messages
9,062
Reaction score
3,935
Location
Wichita, Kansas
So I snagged a UMK3 board off ebay that was "untested - part of a warehouse raid." When I got it and booted it up, it worked, but ALL the roms came up as "red" and it had graphic issues/trouble displaying the character's shadows on the screen.

I did all the normal 'shooting when it comes to graphics glitches ie, swapping the u45 and u47 chips with known good ones, checking all the socket feet on the solder side to make sure none of them were touching, etc.

As a last resort, I started pressing down on everything one at a time until I got to U33 (main processor). When I pressed down on it, the glitches vanished! When I let go, they came back. I brought the board inside and planned on reflowing all the legs of U33. When I got the Iron in hand, I had second thoughts because being a surface mounted chip and all, it's a pain in the ass to reflow all the legs.

So, I decided to do continuity checks on the legs instead. Read everyone of them from the top of the leg to the solder pads and to my amazement, ALL of them were good. Hmm. Head scratcher. I took the board back to the bench and started pressing down on the chips around U33. Nothing. Only time the problem went away was when I pressed down on U33.

Next, I 'twisted' the board gently until the graphic problem vanished again. I KNEW I had contact problem at that point and not an open trace or anything like that. Since pressing down on U33 fixed the problem, I started looking at the chips near it. U34 had some suspicious looking solder joints on some of the legs. I decided to re-flow them. Back to the bench.

Success! Not only did the graphics glitches on the character shadows go away, all the roms now test green/good like normal. It was the third leg on the bottom from the right on U34 that was the culprit.

SAM_418623.jpg


If any of you guys have boards that are reading ALL the roms as "Red/Bad" or character shadow glitches, check out U34. I'm uploading a video chronicling all of the above if anyone wants to watch.

Thanks for reading and watching....

 
Last edited:
very interesting. it'll be nice when I have money again someday, hopefully soon, I'd like to do some repair jobs like these on boards if I get around to it.
 
Back
Top Bottom