IBM 3270 Maintenance Manual page 296

If your system has only one fixed disk drive, go
to page 3-1700-13.
1.
Set the Power switch on the system unit (and
expansion unit, if attached) to Off.
2. Refer to Section 5, "Removal/Replacement
and Adjustments," and disconnect the data
connector (J3) and the control connector (J1)
from fixed disk drive D (see Section 4,
"Locations").
3. Set the Power switch on the expansion unit
(if attached) and system unit to On. If an
error occurs, press the F1 key.
4. When the menu appears, press 0 (RUN
DIAGNOSTIC ROUTINES) then Enter.
5. Depending on the configuration of your
system, questions about attached devices may
appear on your screen. Press Y or N as
required, then press Enter.
CONTINUE
October 1984 3-1700-9