IBM 6150 Hardware Maintenance Manual page 246

Step 5
TNL SN20-9843 (03-27-87) to 75X0152 or 75X0166
Be sure the display signal cable is securely plugged into the system unit.
IS THE DISPLAY SIGNAL CABLE SECURELY PLUGGED INTO THE
SYSTEM UNIT?
YES Record SRN 16-430-600, then go to "Step 6" on page 3-6000-6.
NO This completes the repair.
(3/87) Problem Isolation Charts
3-6000-5