IBM 3270 Maintenance Manual page 87

Recall your POST response.
DID YOU GET ONE LONG AND TWO
SHORT BEEPS?
Note: You may hear other beeps after those
described above. If so, answer this question YES.
YES Replace the display adapter. See Section
5, "Removal/Replacement and
Adjustments. "
NO
If the problem persists after replacing the
display adapter, replace the
keyboard/timer adapter.
3-25-12
Maintenance Information