IBM 3270 Maintenance Manual page 108

Check the continuity between the pins shown
below at the display-adapter side of the top card
connector to ground for the appropriate (PS
and/or APA) adapter.
B03
B14
IS THE CONTINUITY GOOD?
~_-B01
.-----B03
YES Replace the display adapter. See Section
5, "Removal/Replacement and
Adjustments. "
NO
Replace the top card connector.
October 1984 3-90-11