IBM 6151 Maintenance And Service Manual page 277

Step 25
The following FRUs are the most likely to cause a keyboard
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;
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. The keyboard
2. The system board
3. The processor board
4. The power supply
5. The display adapter
6. An adapter for the fixed-disk and diskette drive
7. If installed, the memory expansion option in slot C.
(6/88) Problem Isolation Charts 3-0060-27