IBM 3270 Maintenance Manual page 218

1. Set the Power switch on the system unit (and
expansion unit, if attached) to Off.
2. Remove the diskette-drive logic board (see
Section
5,
"Removal/Replacement and
Adjustments").
3.
Move the read/write head assembly toward
the rear of the diskette drive assembly until it
reaches track
O.
Note: The head is moved under power by the
stepper motor. When you move the head by
hand, you will feel some resistance, but the head
should not bind.
DID THE HEAD MOVE TO TRACK 0
WITHOUT BINDING?
NO
R,eplace the diskette drive assembly (see
Section 5, "Removal/Replacement and
Adjustments").
YES
October 1984 3-600-19