Texas Instruments 990 - Page 135

N
I
w
w
Step _
2
Symptom
Self-test LED does
not light.
Self-test LED
always lighted
Table 2-14. Fault Isolation of Problems Indicated by Self-Test LED
Probable Cause
Lamp or driver
Self-test mode
not selected
Self-test mode
selected by
other controller
Troubleshooting Procedure
Loop on part 1
(El).
See table 2-8.
Scope circuit.
Normal Indication
LED blinks.
See table 2-8.
If Abnormal
Trace back from U83-12
until signal is found. Re-
place faulty component(s).
See table 2-8.
If either controller is in
self-test mode, LED will
be lighted.