Agilent Technologies 856290216 service manual Troubleshooting the Log Amplifier with the TAM

Table 9-1. Automatic Fault Isolation References

Suspected Circuit Indicated		Manual Procedure to Perform
by Automatic Fault Isolation
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