Step 4. Do The External Device Check - IBM 3270 Hardware User's Manual

Step 4. Do the External Device
Check
Do not do this step unless you were told to by
Symptom
1
in the POST Error Chart.
1.
Turn the system unit Off (0).
2.
CAUTION
DO NOT disconnect a coaxial cable during
an electrical storm.
Remove all cables attached to the system unit
except the display or monitor cable and
system unit power cord.
Chapter 5. Locating Problems with Your PC Units 5-15