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As an aid in troubleshooting, critical dc voltages for proper operation are indicated at several
nodes on the accompanying schematic.
If the resolution bandwidths from 3 kHz to 3 MHz have low gain or incorrect bandwidth,
either this board or the A4A4 Bandwidth Filter board may be defective. To determine which
board is faulty, disconnect the 97 cable from A4A8Jl and connect it to A4A6Jl. If the signal
is then 3 to 5 dB lower than expected (CAL OUTPUT is -13 to -15 dBm) or the bandwidth
is 30 to 60 percent wider than expected (1MHz (REsBW_) is 1.3 to 1.5 MHz), then A4A8 is
suspect.
Control line BW5 determines whether the LC filters or the crystal filters are selected. If this
line does not switch, A4A9Q3 on the IF control board should be checked. BW63 controls the
crystal mode resolution bandwidths from 3 kHz to 30 kHz. The LC resolution bandwidths
from 100 kHz to 3 MHz are controlled by BW7. If any of the control line voltages in Note 5 of
the schematic diagram are incorrect, signals from A4A9 IF Control should be checked.
Operation of the AlOdB and A20dB circuitry can be determined by the following method.
Connect a 355D attenuator between the CAL OUTPUT and the input of the spectrum
analyzer. Set this attenuator to 90 db, press Instrument Preset, and key in the following:
Press the @GG?) sweep key and then repeatedly press the DATA STEP @ key. Figure 8
shows the display of a properly working instrument. If either of the first two steps is missing,
the AlOdB or A20dB circuitry is faulty. Note 6 on the schematic diagram indicates the
correct control line voltages from the A4A9 IF Control board.
6
equal to the CAL
OUTPUT frequency
. . . . . . . . . . . . . . . .O Hz
. . . . . . . . . . . . . . 1 kHz
. . . . . . . . . . . . . . . OdB
. . . . . . . . . . . . . . 10 Hz
. . . . . . . . . . . . . . . . 20 s
. . . . . . . . . . -10 dBm
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