IBM 3270 Hardware User's Manual page 134

3. Raise the load lever on disk drive A, insert
the Diagnostics diskette into drive A.
Note Position
of Label
4. Push down the load lever.
5. If you have an expansion unit attached, turn
it On
(I).
6. Turn the system unit On (I).
Chapter 5. Locating Problems with Your PC Units 5-19