Boonton 1121A, Инструкция по эксплуатации

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Section 5 Maintenance
5-26
c. After the Multimeter measurement settles, depress
the OFFSET key to enable the level ratio mode.
d. Disconnect the Calibrator and connect the Model
1121A HI and LOW outputs to the Multimeter input using
the balanced cable and adapters.
e. Set the Model 1121A level to 3.000 volts at a
frequency of 1 kHz and enter special function 75 (50 ohm
output).
f. Note the Multimeter display and adjust A6R23 for a
Multimeter level ratio display of 0.00 ± 1.0 mV.
5-69. A37 CCIR, CCIR/ARM Filter Board Adjustment.
5-70.
The CCIR, CCIR/ARM optional filter board adjust-
ment consist of A37R1`1 Cal. The adjustment sets the
high-pass weighting response and is identical for both
the CCIR and the CCIR/ARM filter applications.
5-71. A37R11 CCIR Cal Adjustment.
Perform the
adjustment as follows:
a. Depress the LCL/INIT key to initialize the instru-
ment.
b. Connect the Source HI and LOW outputs to the
Analyzer HI and LOW inputs using the balanced cable
and adapters.
c. Enable the CCIR filter.
d. Set the Source frequency to 6.300 kHz at a level of
3.000 volts.
e. Enable the Analyzer level ratio mode and depress
the dB key.
f. Set the Source frequency to 1.000 kHz.
g. Adjust A37R11 for a ANALYZER display of -12.20
dB ± 0.05 dB.
h. Set the Source frequency to 6.300 kHz and note
the Analyzer ratio measurement. If the display indication
is not 0.00 ± 0.05 dB then disable the ratio mode and
repeat steps e through h.
5-72. TROUBLESHOOTING.
5-73.
Instrument malfunction will generally be evident
from front panel indications, or IEEE-488 bus responses.
The problems will fall into two general categories: cat-
astrophic failures or selective failure of one subsystem.
5-74.
Catastrophic failures would generally cause the
Model 1121A to be completely inoperative. For instance,
if the microprocessor was not operating properly, the
display would contain meaningless symbols and the
keyboard would not be responsive. Such failures are
usually located in the power supply circuits,
interconnecting cables, and the CPU plug-in board.
5-75.
Selective failures and performance out of specifi-
cation are usually limited to one section of the instrument
and will be evident from manipulation of the front panel
controls. For example, incorrect or erratic distortion
measurements will indicate a fault in the notch filter
circuits on the Notch Filter plug-in board. Further isolation
of the problem requires an understanding of the simplified
block diagrams detailed in the theory of operation section
of this manual and experience in troubleshooting analog
and digital circuits.
5-76. TROUBLE LOCALIZATION.
5-77.
The circuits of the Model 1121A are divided into
three sections: analyzer circuits, source circuits and
interface circuits. The interface circuits consist of the
power supply and digital circuits including the frequency
counter, CPU, display, and keyboard.
5-78. Special Diagnostic Function Codes.
Special
function codes 30 through 33 are provided to localize
selective failures in the source, analyzer and frequency
counter circuits. When entered, these codes continuously
execute the designated test sequence until the LCL/INIT
key is depressed. During the initialization sequence,
analyzer level range and counter tests, error codes are
reported if a fault is encountered. Table 5-23 lists the
ranges, error codes and probable causes to aid in
localizing a fault.
5-79. DAC Test Code.
Contained in the Model 1121A are
three digital-to-analog converters (DAC) which can be
configured to generate a low frequency ramp waveform
using special function 30. A coarse stepped ramp
waveform is usually an indication of missing data bits in
the DAC circuits. The display will indicate the “dac tst”
message when the test is active.
5-80.
The first 12 bit DAC, A7U1, is used to fine tune the
oscillator frequency and is located on the Output plug-in
board. The ramp can be found at A7U2 pin 7 (TP3) and
will have a peak to peak amplitude of 20 volts from -5 to
+14 volts.
5-81.
The remaining 12 bit DACs are used to generate the
rear panel X AXIS and Y AXIS outputs. The ramps from
these DACs can be found at the rear panel recorder
output connectors and will have a peak amplitude ex-
tending from 0 to + 5 volts. The PEN output is toggled
between 0 and + 5 volts at the ramp frequency to provide
an external sync signal.