IBM 6151 Maintenance And Service Manual page 427

3. Close the two board retainers.
4. Do the "Top Cover Replacement" on page 4-13.
Reminder to Service Representative: After you exchange the
Processor Board, notify the customer that the unique identification
number of the system unit has changed. The customer needs to
update the authorization for any program that uses the
identification number for access.
Board Retainer
AJZBFOZO
(6/88) Removal and Replacement
4-17