IBM 3270 Hardware User's Manual page 59

4. If you have the expansion unit or any other
optional units attached, turn them on.
Note: If you are turning on the system unit
for the first time, you should not have
any other options attached.
5. Make sure that the load lever on diskette
drive A is up, and insert the Diagnostic
Diskette.
Note Position
of Label
2-42 Book 1 - 3270 PC Work Station User's Guide