Sounds like a good idea to check the voltage conditions. Need to get myself a new multimeter - I had an old one which seems to have broken.

The ROMs seemed to be fairly corrosion free, although I'll check again next time I open the Mac up.

There were different logos on the two sets of ROMs, so it does seem like two different companies sourced them. I'll send some pictures of both sets in case anyone is interested.

Forgot to mention that I also tried the bad ROMs in the working 128 logic board, and it did not work - in fact it resulted in a slightly different error condition. With the bad roms in the otherwise working 128 board, I got a checkerboard pattern instead of vertical stripes. I'll check those roms back in the repaired board and see what I get.

Next steps will be to check if just one or both ROMs are bad. Also attempted to rehabilitate the seized-up internal floppy drive last night. Got the parts de-greased and moving again, but there seems to be something else wrong with the drive. The red LED does come on, but when disks are inserted there is just a mournful quiet chunk..... chunk... chunk.... sound and no movement. I'll look through the repair book again to see if this case is mentioned.

Does anyone happen to know the pinout for the 128 roms? I may look into what steps would need to be taken to get a modern-day PROM to work as a substitute.

Thanks again!