IBM 3270 Maintenance Manual page 220

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.
4. Reinstall the diskette-drive logic board (see
Section 5, "Removal/Replacement and
Adjustments").
5. Set the Power switch on the expansion unit
(if attached) and the system unit to On.
6. Check that the voltage at pin 26 on the signal
cable connector is approximately 5.0 V dc at
the start of POST then decreases to
approximatelyO V dc as the LED lights at the
end of POST.
WAS THE VOLTAGE APPROXIMATELY 5.0
Vdc AT THE START OF POST?
NO Go· to page 3-600-34.
YES
October 1984 3-600-21