I recently bought a BK2K which was having issues with the top display. After further inspection battery leakage was found on the pins for U41 and U42. After doing some cleaning up with vinegar, the display worked normally but the music stopped working.

The board was taken out and cleaned more thoroughly as there was still quite a bit of build up on the pins closest to the battery holder. We also took the battery holder off, cleaned and replaced with a remote holder. Using the schematics we tested the pins on both of these chips that were in the path of the leakage and found two broken lines and repaired them (Pin 18 on U41 to SRC1 Pin 2 and Pin 17 on U42 to SRC3 Pin 9). After plugging the MPU back in and staring up the machine it started as normal with the display working fine. However, there is still no music. I also noticed that it seemed like the sounds didn’t match up the way they were supposed to (wrong sound effect when hitting the pop bumpers etc). I tried pressing the test button on the MPU (SW1) to see if that revealed anything but instead of hearing tones I heard the “Ahhhhh” Chorus sound effect going off over and over. Any ideas what to try next? Maybe go back and check all pins on the two chips? I did have music and sound that was correct before cleaning the board, so I don’t think its going to be the roms.

Yeah I think we are going to check the traces for all pins on U41 and U42. More than likely we missed at least one other since we didn't check all of them. Seeing as though the sound did work before cleaning off the corrosion, I'd think the corrosion itself was keeping these traces working.

Game is back up and running! There were 4 bad traces going to the U41 and U42 chips, and one other that was real close to being broken. Repaired all 5 via very thin wires on the underside of the MPU board. Hopefully we neutralized all the corrosion so it doesn't happen again. If so at least we know where to look and test!