IBM 6151 Maintenance And Service Manual page 202

Step 24
The following FRUs are the most likely to cause a failure in the
fixed-disk and diskette drives.
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;
then 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. An adapter for the fixed-disk and diskette drives
2. The cables for the fixed-disk and diskette drive
3. The IBM High Capacity Diskette Drive
4. The system board
5. The processor board
6. The power supply
7. The display adapter
8. If installed, the memory expansion option in slot C.
3-0060-26 Service Manual