IBM 6151 Maintenance And Service Manual page 407

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Step 9
One of the remaining FRUs is failing.
1. Set the power switch on the system unit to Off.
2. Exchange and test the FRUs one at a time in the following
order:
a. The processor board
b. The system board
c. The adapter for the fixed-disk and diskette drives
d. The display adapter (If the display adapter is the Megapel
Adapter, exchange the processor; then the controller.)
e. The diskette drive
f. If installed, the memory board in slot C.
3. Be sure the power has been off 30 seconds; then set the power
switch on the system unit to On.
4. Try the failing procedure.
DID YOU FIND THE PROBLEM?
NO Try a new set of diagnostic diskettes. If the problem still
occurs, contact your service support person. Otherwise, go
to "Step 12" on page 3-9860-12.
YES
Go to "Step 12" on page 3-9860-12.
(6/88) Problem Isolation Charts 3-9860-9