IBM RT PC 10 Hardware Maintenance And Service page 82

Step 14
The number "99" in the two-digit display indicates the keylock is in the
Locked position. Look at the keylock.
IS THE KEYLOCK IN THE LOCKED POSITION?
NO
Record SRN 11-630-100, then go to "Step 2" on page 3-6.
YES
Set the keylock to Unlock, then go to "Step 2" on page 3-23.
Problem Isolation Charts
3-37