ADC/lnterface Check

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:

nAmplifier and oscillator dc current draw by monitoring the voltage across a resistor of known value.

nOscillator tune voltages ensuring proper operation of phase/frequency detectors and loop integrators.

nStatic bias voltages.

If probing a connector for a check yields a “FAIL” indication, select the desired check using either the knob or step keys and press More Info. A description of the function checked (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

General Troubleshooting 6-13