On Wed, 3 Feb 2021, Fred Cisin via cctalk wrote:
. . .
Then try cylinder 36.
If the disk had been written on a 48tpi 35 track drive (SA400/SA390 used on
TRS80 and Apple), then cylinder 72 of a 96tpi/cylinder 36 of 48tpi would not
have been used. If cylinder 72 does not read, but 36 gives a valid read that
identifies itself as track 18, then it is most likely from a 35 track 48tpi
drive, such as SA400.
That second attempt should have read cylinder 54/27, not 36/18
Again, to try to do most of the analysis on the less likely to be in use
tracks.
THIRD attempt should be 36/18
Then, if you are feeling bold, cylinder 0
Cylinder 0 may be a different format than other parts of the disk, such
as the continuation of FM for system tracks of CP/M even after the rest
of the disk went to MFM.
Watch for what looks like it might be a DIRectory in the low tracks, OR
for some formats the MIDDLE tracks (17,20, etc) for variants of TRSDOS,
Microsoft Stand-Alone BASIC, etc.
