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Table 9-1. Automatic Fault Isolation References
Suspected Circuit Indicated
by Automatic Fault Isolation
Manual
Procedure to Perform
Check Cal Oscillator on A4 Assembly
Troubleshooting the Cal Osc with the TAM
Check Input Switch on A5 IF Assembly
Troubleshooting A5 with the TAM
Check Linear Amplifiers on A4 Assembly
Linear Amplifiers
Check Log Expand on A3 Interface Assembly Refer to “Log Expand” in this chapter
Check Step Gains on A5 IF Assembly
Step Gains
Check Video Offsets on A4 Assembly
Video Offset (steps 1 through
4)
Check VIDEO OUT on A4 Assembly
Video Output
Troubleshooting
the
Log
Amplifier
with
the
TAM
Manual probe troubleshooting tests several dc bias points and signal path voltages. A dc
bias is measured in the limiter and a fault here indicates a broken limiter stage. Signal path
voltages are measured at the input, after the video amplifier in the linear path, after the offset
and gain compensation circuits in the log path, and after the video offset.
The cal oscillator on A4 is used as an input to the log amp for the purpose of measuring
gains. Faults in the signal path voltages indicate broken circuitry in prior stages. This
technique locates dead stages, but might not report slightly degraded ones. Both
+15
V and
-15 V are measured. The revision code is on
Jll.
Troubleshooting
A5
with
the
TAM
Manual Probe Troubleshooting calculates stage bias-currents which test the operation of the
IF chain. (This technique locates dead stages, but might not report slightly degraded ones.)
DACs that are monitored are listed below:
IFDACl
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U812
IFDAC2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U813
IFDAC3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U809
IFDAC4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U807
IFDAC5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U810
IFDACG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..A5U806
9-4 IF Section