LO Control Check
The LO control check verifies 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 Low Band Check
The TAM tests the operation of the A8 low band mixer, the A9 input attenuator, the A10
YIG-tuned filter/mixer (RYTHM), the second IF distribution, the third converter (A15), 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, if present, for the third LO while simultaneously decreasing the first LO frequency
by 2 MHz. If a signal can now be detected, troubleshoot the third LO driver amplifier on the
Al5 RF assembly.
Manual Probe
Troubleshooting
Manual probe troubleshooting probes the instrument test connectors to perform the following
types of measurements:
n Amplifier and oscillator dc current draw by monitoring the voltage across a resistor of
known value.
w
Oscillator tune voltages ensuring proper operation of phase/frequency detectors and loop
integrators.
w
Static bias voltages.
w
DAC output 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
Maze
Info. A description of the function checked
(with measured and expected voltages or 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
printer is connected, press Print Page to provide a hard copy of the currently displayed
screen (the
softkey
labels will not be printed).
Each test connector has fifteen pins (one pin is missing to act as a key). The pins contain
eight measured signal lines (measured signal lines denoted as MS1 through MS8), one input
signal line
(OSl),
one ground, and five pins encoding a five-bit connector address.
The TAM needs to probe each assembly revision connector once; subsequent readings are not
necessary. It is possible, for example, to probe the A5 IF assembly, then the A4 log amplifier
assembly, and then return to A5 without having to re-probe A5 revision connector. However,
the revision connector must be re-probed if the spectrum analyzer is returned to normal
operation and then back to TAM control. (This is also true if the spectrum analyzer is turned
off.)
General Troubleshooting
7-l
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