HP 8560E, Service Manual

Page: 296 / 665

Chapter 6 295
General Troubleshooting
Using the TAM
ADC/Interface 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 A13 second converter.
AFI also checks the flatness compensation amplifiers (part of the A15
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 (Option 008 only) 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
A15 RF assembly.