NeoGeo MV4F - White screen / Lines in graphics - Repair Log

[srarcade]

Purchased a used MV4F that was marked non-working with the intent of fixing it to add a 4 slot to my collection. State when received was white screen when powered on.

Fix 1: Checked battery first- original battery was in place and corroded several traces nearest to it and below it. I tested all pins and traces running in the bad area on the large 64? pin connector to the right of the battery, found 5 bad traces from the corrosion. 3 traces were directly to the edge connector on pins 8 and 9. Applying jumpers to fix traces got the board to power on and run games but there were lines in the background graphics. Audio is also very poor.

Fix 2: Just probing around the output line buffers (74F253) to make sure they were all alive I found one was dead. Turned out the pin #1 on 7A was broken, it looks like this chip took a hit at some point and it slightly bent it and broke the leg. Applied a little solder to fix. Lines were now fixed for slots 1, 2 and 3. This is when I noticed slot 4 still has lines but they are on the sprites as well as in the background.

Fix 3: I looked closer into the input/outputs of all the 74F253s. All chips except for D1 appeared to be working correctly. On D1, pin #9 (output b) was stuck high only when slot #4 was active. Checking the b input on D1 pin #13, it was null. I followed the trace back to pin B21 on slot 4. The trace was broken although it looked fine to the eye. I made a jumper, lines now gone from slot 4. All slots looking great now!

Fix 4: Low audio/distortion- replaced all caps in audio area, sound is now working perfect.

Fix 5: Remote installed a battery holder and a 1/2AA battery, glued it outside the case, no more leaks.

[channelmaniac]

Those caps are a pain, no?

Nice fix!