Apple A9M0106 800k External Floppy Drive Connectors

I use this 800k drive with a Mac 512k that has the original 64k ROMs. Pins 9 (-12v) and 20 (speed) are disconnected for compatibility because my Mac's internal floppy drive is still 400k (see pages 193 and 194 of Larry Pina's Macintosh Repair & Upgrade Secrets book).

 

This external 800k drive works well except for one odd problem. The red LED on the floppy drive lights up every 2 seconds when no disks are in the drives (at boot time). The Mac seems to scan the drive continually until a disk is inserted (I can hear a small motor noise from the drive every 2 seconds when the LED flashes). This seems odd since that 800k drive is supposed to be supported by the Mac 512k. I am aware of the HD20 init, but that is only required to read/write 800k disks. Once I boot the Mac, I can read/write 400k disks in this 800k drive without any init installed. 800k disks, of course, only work with the HD20 init. I believe this to simply be a minor incompatibility with this drive and the 64k ROMs, as opposed to a unique problem specific to my external drive alone.

 

The drive mechanism is a red-labeled SONY MFD-51W-03. Voltages at the 800k drive connector measured 4.75v~4.78v, and 11.99v.

Done