IBM 6151 Maintenance And Service Manual page 251

IBM 5151 Personal Computer Display PIC 5400
Use this PIC to get an SRN when there is a problem that prevents
you from reading the display screen easily, the two-digit display is
blank, and the system unit power indicator is on.
Step 1
1. Turn the Brightness and Contrast controls fully clockwise.
2. Look at the display screen.
AJZB193
IS THE BACKGROUND OF THE DISPLAY SCREEN
LIGHTED?
YES Go to "Step 3" on page 3-5400-3.
NO Continue on the next page.
(6/88) Problem Isolation Charts 3-5400-1