Response from Jonathan: Very interesting issue. We would typically think that this would be caused by some sort of rom chip issue. Since you’ve replaced the rom chips, the next place to look at would be the ram chips. You will need a tester in order to test ram chips. Many rom burners can be used to test ram chips but they might need additional software and/or adapters to perform this task. You could also try plugging the ram chips from your Donkey Kong into a different board that uses the same ram chips. Pac Man would be a good example of a game that also uses a lot of the same ram chips as Donkey Kong. Of course, you could try just replacing the ram chips all together. They are fairly inexpensive (less than $10 a piece) and might be less of a hassle than trying to find a ram chip tester.

Another thing you might want to consider is your power supply. Make sure your power supply is giving the correct voltages to the board. Incorrect voltage can cause all sorts of issues. You might even consider going with a Power Supply Conversion Kit as this will make it much easier to test and maintain the DC voltages in the future.

Hope that helps. Thank you for your question and good luck with your repair.