Floppy drive oddity? (TEC FB-503)

Picked up 6 Morrow MD computers this past weekend. All appear to work, however I have one with floppy drive trouble ... The drives in question are TEC FB-503 1/2 height 5.25" drives. Only one of the machines has these drives. What is odd is that both drives in the one machine will not read diskettes (report disk error - won't even boot). Only one machine has these drives - when it failed to boot, I first tried cleaning it - no improvement - then tried swapping for 'B' drive - still no improvement - now thinking that diskette controller is faulty. Then I swapped in a Panasonic drive from my parts shelf, and voila - boot & access disk no problem. Seems really odd that two identical drives would fail so completely in the same way when all of the other 10 drives appear to be OK. I thought that perhaps they were 80 track drives or some such, however Issue #1 of the "Morrow Owners Review" has an artical about the floppy drives used in the MD's, and it lists the TEC/NSA 5503, which looks like these drives - Can't say for sure if they are the same ones, as the model number stated does differ slightly from what is on the drive plate, but if they are the same, the artical makes no mention of anything special about them... Does anyone know anything about these drives? Are they 80 track or otherwise "odd"? Are they known to have a high failure rate (especially with age)? Any info would be appreciated. Regards, -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Vintage computing equipment collector. http://www.parse.com/~ddunfield/museum/index.html