IBM 6151 Maintenance And Service Manual page 278

Step 26
The following FRUs are also likely to cause a failure.
Exchange the FRUs that have not been exchanged in the following
order. Test each FRU by running System Checkout. If you
identify a failing FRU, use the removal and replacement
procedures in the section that applies to the FRU and exchange it.
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. The system board
2. The processor board
3. If installed, the memory expansion option in slot C
4. An adapter for the fixed-disk and diskette drive
5. The display adapter
6. The power supply.
3-0060-28 Service Manual