Hi, All, Tangential to my Mac128K repair, I now have an OA-D34V-22 drive but my Mac128K board came with -A ROMs, as I have mentioned previously. I have found pictures of various models of this drive, and I know about what models work with what ROMs, but what I haven't been able to find out is what changed that old firmware doesn't work with newer drives. For search terms (and later documentation of this topic), here's the matrix... Original rev 64Kbyte ROMs, P/N 342-220-A / 342-221-A OA-D34V works OA-D34V-22 does not work OA-D34V-02 does not work Later rev 64Kbyte ROMs, P/N 342-220-B / 342-221-B OA-D34V works? OA-D34V-22 works OA-D34V-02 works motor, but I haven't turned up any details. My guess is the original stepper pulse frequency or pulse width doesn't drive the motors on the newer drives correctly, but does anyone here know what the changes are and why? My solution to what hardware I have is still going to be to replace the -A ROMs with -B ROMs, but I just wanted to learn more. Thanks, -ethan