IBM 6151 Maintenance And Service Manual page 151

Step 19
Some problems prevent the diagnostic diskette from loading and
the Operating System loads instead.
Look at the display and determine if a screen from the customer's
operating system is displayed. If needed, ask the customer for
assistance in determining the above condition.
IS A SCREEN FROM THE CUSTOMER'S OPERATING
SYSTEM DISPLAYED?
NO Go to "Step 21" on page 3-0030-21.
YES
Continue on the next page.
(6/88) Problem Isolation Charts 3-0030-19