IBM 3270 Maintenance Manual page 325

Note: If you have only one fixed disk drive,
continue on the next page.
1.
Set the Power switches on the system unit
and expansion unit to Off.
2. Disconnect the power connector from the left
fixed disk drive.
3.
Set the Power switch on the expansion unit to
On.
4. Set the Power switch on the system unit to
On.
Power Connector
DID THE SYMPTOM REMAIN?
NO Replace the left fixed disk drive assembly
(see Section 5, "Removal/Replacement and
Adjustments").
YES
3-1800-10 Maintenance Information