Modifying a Floppy Drive for GRiDCase computers

Back to Hacking the GRiDCase 1500 Series

The GRiDCase 1520 and 1530 portable computers use 1.44 MB 3.5″ floppy drives but they very slightly from the most common generic drives of that time.  Here’s how I was able to adapt a standard drive.

I used an Alps drive because I was able to find which pin of the SD705A controller provides the needed signal.  Really any floppy drive should be adaptable as long as you can identify the signal sources.

Modifications of a standard floppy drive for GRiDCase 1500 series compatibility.
Modifications of a standard floppy drive for GRiDCase 1500 series compatibility.

The changes required are as follows

  • Rewire the pin 34 signal from DISK CHANGE to READY
    This required cutting the DISK CHANGE trace feeding pin 34 then running a jumper wire to the READY pin of the controller.  If your drive is different you will need to find a datasheet for it’s controller to identify the source of the READY signal.
  • Change ID to 0 (if it’s not already)
    Some drives have pluggable jumpers, others have solder jumpers (like the one shown).