IBM 6151 Maintenance And Service Manual page 147

Step 15
The number 99 in the two-digit display indicates the keylock is in
the Locked position. Look at the keylock.
AJZB163
IS THE
KEYLOCK IN
THE
LOCKED POSITION?
NO Record SRN 11-630-100; then go to "Step 33" on
page 3-0030-33.
YES Set the keylock to Unlock; then go to "Step 2" on
page 3-0030-2.
(6/88) Problem Isolation Charts 3-0030-15