IBM 3270 Maintenance Manual page 224

5.
Set the Power switch on the expansion unit
(if attached) and the system unit to On.
6. Observe the movement of the head assembly.
Track 39
Track 0
Type 1
Track 39
Type 2
DOES THE HEAD ASSEMBLY MOVE TO
TRACK 0 AND THEN AWAY FROM IT
BEFORE THE END OF POST?
NO Replace the diskette-drive (see Section 5,
"Removal/Replacement and Adjustments").
YES
October 1984
~600-25