Well if you can format/read HD floppies on the machine your using, but they cant be read on another one, your heads are out of alignment. the track alignment is alot tighter on HD than DD. So DD can work fine (mostly) but HD be dead.

Only way I know of realigning the heads is let the motor sit and run on track 0 of an HD disk. (a readable one in all machines). Then measure the head output with a scope. Unlock and twist the stepper motor until your amplitude is at its maximum. Then tighten the stepper motor locking screw.

Voiala.