IBM 3270 Maintenance Manual page 330

One of the option adapters plugged into the
expansion board may be failing.
1.
Set the Power switch on the system unit and
expansion unit to Off.
2. Install one option adapter.
3. Make sure the Diagnostics diskette is
inserted.
4. Set the Power switch on the expansion unit to
On.
5.
Set the Power switch on the system unit to
On.
6.
If an 1801 error code occurs, press PF1 to
continue.
CONTINUE
October 1984 3-1800-15