Model III Disk Drive Problem

[Moonferret]

Hi Folks!

Just started work on a Model III with an interesting problem. The machine can boot an OS fine from disk but when formatting or writing to disk, It's unable to read past track 20. I've swapped known good drives in (Even tried an HXC). Also swapped the 1793 controller IC but no change. Issues is definitely with the disk controller board but I'm having trouble figuring out why it would fail at this point. Any suggestions?

Cheers,
Dave

 

[Moonferret]

Forgot to add, the head does move across the entire disk surface.

 

[Moonferret]

Fixed it! Followed the procedure on Page 45 of the M3 technical manual to adjust one of the pots on the drive controller PCB. I wasn't getting the correct 2Mhz square wave needed for the data separator