HP 8560A

Table 8-1. Automatic Fault Isolation References
Suspected Circuit Indicated
by Automatic Fault Isolation
Check Cal Oscillator on A4 Assembly
Check Input Switch on A5 IF Assembly
Check Linear Amplifiers on A4 Assembly
Check Log Expand on A3 Interface Assembly
Check Step
Gains on A5 IF Assembly
Check Video Offsets on A4 Assembly
Check VIDEO OUT on A4 Assembly
Manual Procedure to Perform
Troubleshooting A4 Cal Osc with the TAM
Troubleshooting A5 with the TAM
Linear Amplifiers
Refer to “Log Expand” in this chapter
Step Gains
Video Offset (steps 1 through 4)
Video Output
Troubleshooting A4 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 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
8-4 IF Section