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Write Precompensation Adjustment for Zenith Z-100 needed for formatting errors


Veteran Member
Jan 29, 2014
As I mentioned on another thread recently, I was having issues with formatting both 8 inch and 5 inch floppies. The 8 inch would appear to format correctly but then give me a FAT error when I attempted to copy
files to it:

Then when I formatted 5 inch floppies, I would get an error at track 23. The odd thing was, the Z100 diagnostics would format and pass the entire disk !! This had me doing some major head scratching.
I came across a Z100 newsgroup post about the track 23 problem and that write precomp adjustment of R3 fixed the issue. So I looked in the Z-100 Technical manual and on page 6.9 it says:
"Heath/Zenith software precompensates tracks 23 and greater". So I looked at R3 on my Z207 board which is the pot PRECMP1 with the red glue in this photo:

I also discovered the pot turned easily so the glue was broken. I rotated it clockwise to match the other PRECMP2 control and then noticed the glue pattern lined up !! Now format successfully completes and verifies all tracks
on both size disks. Now I can sleep easier tonight ...

Larry G