IBM 6151 Maintenance And Service Manual page 193

Step 16
One of the FRUs still installed in or attached to the system unit is
failing. The following list is in the most to least likely to fail
order.
If you have not exchanged it already, use the removal and
replacement procedures in the section that applies to the FRU and
exchange it. Test each FRU by running the failing diagnostic
checkout. If you identify the failing FRU, go to "Step 28" on
page 3-0060-30. If you cannot identify a failing FRU, contact your
service support person.
Exchange the following FRUs in the order listed:
1.
FRUs required to run the failing diagnostic checkout.
2. The system board.
3. The processor board.
4. A display adapter.
5. If installed, the memory expansion option in slot C.
6. The adapter for the fixed-disk and diskette drive.
7. The power supply.
(6/88) Problem Isolation Charts 3-0060-17