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The keyboard interface and strobe-select circuitry must be functioning correctly, since these
are required to operate the TAM. The TAM checks the ADC by attempting to measure three
signals from three different locations. This ensures that an open or short in one cable will not
hide the fact that the ADC is operating satisfactorily.
The analog bus (W2 Control Cable) is checked by sending data out on the data lines and
reading the data back. If this check fails, disconnect one board at a time and rerun AFI
to determine if an assembly causes the problem. If the fault remains with all assemblies
disconnected from W2, troubleshoot W2 or the A3 Interface Assembly.
IF/LOG Check
The TAM uses the Cal Oscillator on the A4 assembly as the stimulus for checking the IF
Section. If the signal is undetected, the TAM repeats the test with a signal originating from
the RF Section. Presence of this signal through the IF indicates a faulty Cal Oscillator.
LO Control Check
The LO Control Check verifies test that all phase-lock loops (PLLs) in the Synthesizer
Section lock. (Some oscillators are checked to ensure that they will lock outside their normal
operating frequency range.) The TAM also performs an operational check on several DACs in
the Synthesizer Section.
RF Check
The TAM tests the operation of A8 Low Band Mixer, A9 Input Attenuator, Second IF
Distribution, and most of the Al3 Second converter.
AFI also checks the Flatness Compensation Amplifiers (part of the Al5 RF Assembly),
ensuring that their gain can be adjusted over a certain range.
If no signal is detected through the RF Section, AFI will substitute the 298 MHz SIG ID
oscillator for the 3rd LO while simultaneously decreasing the 1st LO frequency by 2 MHz.
If a signal can now be detected, troubleshoot the 3rd LO Driver Amplifier on the Al5 RF
Assembly.
Manual Probe Troubleshooting
Manual Probe Troubleshooting probes the instrument's test connectors to perform the
following types of measurements:
Amplifier and oscillator dc current draw by monitoring the voltage across a resistor of
n
known value.
Oscillator tune voltages ensuring proper operation of phase/frequency detectors and loop
n
integrators.
Static bias voltages.
n
If probing a connector for a check yields a "FAIL" indication, select the desired check using
either the knob or step keys and press
(with measured and expected voltages/currents) is displayed with a list of additional areas
to check. These areas can sometimes be checked by looking at another TAM connector, but
usually require manual troubleshooting techniques to isolate the problem further.If an HP-IB
A description of the function checked
More Info.
General Troubleshooting 6-13
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Troubleshooting
