I am not that familiar with Nintendo PCBs or your repair experience. Maybe read through the thread linked below and then report back what steps you have taken to diagnose the problem.
Its certainly a board issue. After verifying voltages I would pull and verify all the roms. Could be as simple as a bad rom, anything else and you will probably want to seek someone with nintendo board repair experience.
That is a rom issue in the 7X series Eprom on the video board. Have you tried pulling those roms and cleaning the legs. Push down on each rom with your finger maybe one came slightly loose.