Spent a bit of time going through some Donkey Kong and DK Jr. boards I've had sitting for a while. Not included in these repairs are a few boards that had bad roms and/or bad rom sockets. Boards with bad roms and/or a bad socket are fairly common in my experience and the first thing you should look at. Also check the pots on the video boards as they tend to crack if the board has been banged around, the board will look out of sync if the pots are bad.
Donkey Kong Jr. CPU Boards
Jump Sound off Pitch, No Walk Sound (2/8/17) – This was a board I just fixed with the constantly thumping sound. Didn’t notice it had another sound issue until further play testing. Replaced caps in jump section as well as some other caps in sound section, but no change. Replacing 4020 IC at 6L fixed the problem, thanks to Scott Brasington for documenting this repair online.
Jump Sound Off Pitch (2/7/17) – Jump sound was out of pitch, just not right. Replaced C24, C23 and C22 but no change. Closer inspection showed pin 9 of 8L was never soldered properly through the board. The leg was bent and didn’t make it through the solder hole. Looked like this was from the factory, the jump sound probably never worked properly. Was able to remove solder from hole, run a small metal lead through the hole and solder it to the leg to fix the problem.
Thump Sound Constantly On, No Music (2/7/17) – The “thump” sound from Donkey Kong jumping at the beginning of stage was constantly playing, no music was present. Initially thought this was a bad transistor as that seems to be common issue when sounds are stuck “on”. All sound transistors tested good, swapped out the 8035 and sound rom, no change. Recapped the sound section just in case, but no change. Grabbed the logic probe and starting probing around before the 8035 and found pin 10 at 74LS04 at 6J was stuck low (it should have been high). Replaced 74LS04 at 6J to fix the problem.
All Low Sounds (2/7/17) – Sounds were present, but very low. Noticed R1 was burnt, replaced it, no change. Pulled Q1 and it tested bad, replacing C1815 at Q1 fixed the problem.
Donkey Kong CPU Boards
Garbage on Screen (1/31/17) – CPU boardset booted to garbage, went to pull Z-80 and test roms with Fluke 9010a. Original Z-80 socket was replaced and the replacement socket didn’t look very high quality and poorly installed. Removed the socket, cleaned up the area as best I could and installed a new socket, board now works.
Garbage on Screen (1/31/17) – Fairly clean CPU boardset, complete, but boots to garbage. Used Fluke 9010a to test roms and found program roms at 5C and 5F where bad.
One background sound during intro sequence out of pitch (after DK thumps) – recapped entire sound section, but no change. Replaced LM724 at 8K and that fixed the problem.
Board had Mario Heads and Bottom on Screen (2/6/17) - Kind of an odd problem, it would boot up fine, after a couple minutes Mario's head and bottom would appear on the screen in the four corners (see picture). Used some freeze spray to hit the chips and after spraying 2148 ram at 6R the picture would clear up again. Replaced ram at 6R to fix the problem.
Sprites had horizontal lines (2/3/17) – Board looked close, but the sprites had horizontal lines running through them. Also a small horizontal line was on the title screen near the middle left hand-side. Board had a fresh set of roms, swapping them into a working board, found rom at 7D to be bad. Rom tested fine in burner, but didn’t work in the board.
No Sprites (5/18/12) – Board came up, but no sprites. Checked outputs at 3E and found a signal missing. Replaced 74LS163 at 3E to fix the problem. Thanks to Mike at Mike’s Arcade for this one, he had already documented the problem so it was easy to find.