I can't recall the exact values but Google seems to suggest 180 Ohm. I had remembered 220 for some reason, though. Unless the resistors failed open circuit, I doubt they're directly responsible for the issues. However, I have seen signal degradation in the MMU ribbon cause a lot of cartridge issues in the past (usually because of wear and tear on the cable if the board has been removed several times). It would be well worth completely replacing the MMU cable first, and then the OS ROM cable before trying to diagnose issues with the U1MB board itself.