mtools / double-density floppies / old PC problem

[Conrad Newton <conrad.newton@broadpark.no>]

This is not strictly a debian question, but I'm afraid
this list is my best hope for answering a question that 
may otherwise go unanswered.

I do some word-processing on an old PC (1980s) whose
operating system runs off of double-density diskettes.
MS-formatted double density diskettes are also the means 
of storing the files.

There is no problem to take the diskettes, and copy the
files over to Debian, but the reverse direction appears 
to be problematic.  That is, if I copy the files from 
the modern computer (e.g.  with mcopy) and then try to read 
them on the old PC, the diskette is no longer readable.

I know that I have managed to copy from new -> old in
the past with success, but I cannot remember how,
and it baffles me that mcopy no longer seem to work.

The diskettes on which the copy operation new -> old
have NOT been performed work fine, so it does not appear 
to be a hardware problem.  The copy (actually mcopy) 
operation appears to be the source of the trouble.

Any idea why this might be happening?  Even better,
does anyone know a fix?

Thanks, Conrad