Chapter 8 409
IF Section
Troubleshooting Using the TAM
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 J11.
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:
IFDAC1 .........................................................................A5U812
IFDAC2 .........................................................................A5U813
IFDAC3 .........................................................................A5U809
IFDAC4 .........................................................................A5U807
IFDAC5 .........................................................................A5U810
IFDAC6 .........................................................................A5U806
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