For soft-sectored floppy disks you have to jumper to 850 mode and for hard-sectored disks to 851 mode.

I use the following jumper options. Blue dot: Trace or jumper plugged

I have another SA851 since August 2023. It was so new that I couldn't even open it at first! Yes, that's right, the drive definitely couldn't be opened. I unlocked it as usual with the little top mechanism, but the bottom latch wouldn't move a micron. After about five minutes I knew why. The whole mechanism was still secured by a screw. Learned something again.

There are different versions of the R/W heads. One is the well-known „tunnel erase“ (TE) and the other is the „straddle erase“ (SE). I only know the SE from the old Shugart drives; the TE from all TEAC drives.

1. (↑) Shugart SA850/851, Service Manual, 1980
2. (↑) Shugart SA850/851, OEM Manual, 1980

• Shugart 850/851 OEM Manual (en), 1982 (1,8 MByte)
• Shugart 850/851 Service Manual (en), 1980 (12,8 MByte)
• Shugart 850/851 (another) Jumper Configuration Description