IBM 5150 Hardware Maintenance Manual page 93

Press (Enter). This
will
return you to an all black
@
screen. Selecting the all black screen will place a signal on pins
3,4,5, and 6 of the 9 pin connector of between 0.0 and 0.5
Vdc. At the phono-jack connector, the voltage between the
0
two test points should be 0.0 and 0.9 Vdc. Measure the
voltage present at pins 3,4, 5, and 6 of the 9 pin connector
and the voltage between the center and outer edge of the
phono-jack.
o
o
WERE YOU ABLE TO READ THE PROPER VOLTAGE?
NO
Replace your Color/Graphics Monitor Adapter. See
Section 3, "Removal/Replacement."
YES
500-22