IBM 3270 Maintenance Manual page 228

1.
Set the Power switch on the system unit (and
expansion unit, if attached) to Off for 5
seconds.
2. Set the Power switch on the expansion unit
(if attached) and the system unit to On.
3. Check that the voltage at pin 16 on the signal
cable connector is approximately 5.0 V dc at
the start of POST and decreases to
approximately 0 V dc before the "beep" at the
end of POST.
DID THE VOLTAGE AT PIN 16 DECREASE
TO APPROXIMATELY 0 Vdc?
NO
Go to page 3·600·34.
YES
October 1984 3·600·29