Model
8901B
Service
@
Input Mixer and
IF
Check
NOTE
This check assumes that
(J5)
Local Oscillator Tuning Check
and
@
Local Oscillator Level Check
give positive results.
1.
Set signal generator
to
approximately
20
MHz CW at
0
dBm. Connect
its
RF output to the
Modulation Analyzer’s INPUT.
2.
Connect an ac coupled oscilloscope to rear-panel
IF
OUTPUT. Switch the input impedance of
the oscilloscope to
50R
or
terminate the input in
500
using a tee.
3.
Press the blue key, then press INSTR PRESET (the AUTOMATIC OPERATION key) to preset
the instrument. Key in
1.3
SPCL
to
set the attenuation range
to
20
dB.
Key in
20
MHz on the
Modulation Analyzer to manual Tune. The waveform should be a sinewave
80
to
126
mVpp with
a period of between
645
and
690
ns (that is, nominally
1.5
MHz). If faulty, see Service Sheets
BD3,
5,
and
9,
and check the Input Mixer,
IF
Filters,
IF
Amplifiers, and
FM
IF
Buffer.
4.
Key in
3.1
SPCL to set the
IF
to
455
kHz. The waveform should be
a
sine wave
67
to
106
mVpp
with a period of
2.19
to
2.21
ps
(that is, nominally
455
kHz).
If
faulty, see Service Sheet
5
and
check the
455
kHz Wide Bandpass Filter
(2314A
to
2636A)
and in addition the First and
Second
IF
Amplifiers
(2642A
and
Aboue).
(J7)
Power Meter Check
1.
Perform
Performance Test 8-Power Meter
in Section
4.
If
the Zero Set
test
fails, see Service
Sheet
2
and check the Zeroing DAC. If the Range-to-Range
Error
test
fails, see Service Sheets
1
and
2
and check the Attenuators, Amplifiers, Synchronous Detector, and Noise Filter.
If
the
Accuracy within a Range test fails, see Service Sheet
1
and check the Synchronous Detector.
@
Power Reference Oscillator Check
1.
Perform
Performance Test
6
or
7-Power Reference
in Section
4.
(Either of the
two
procedures
can be followed.)
If
faulty, see Service Sheet
3.
(J9)
Sensor Module Switch Control Check
1.
With no power sensor
or
sensor module connected
to
the SENSOR connector, connect a high-
impedance, dc coupled oscilloscope
to
pin A
of
the SENSOR connector. (See Service Sheet
1
for
the location of pin A.)
2.
Set the oscilloscope sweep to
20
ms per division and vertical sensitivity to
1OV
per division.
3.
Alternately press RF POWER and FREQ. Each time a new key
is
pressed, the signal on the
oscilloscope ,display should drop
to
-15V
for approximately
30
ms, then return to OV.
If
faulty,
see Service Sheet
2
and check the Sensor Module Switch Control.
4.
Connect an ohmmeter to pin B of the SENSOR connector. Press FREQ, then press RF POWER.
The resistance should be less than
5R
for each setting. If faulty, see Service Sheet
2
and check
the Sensor Module Switch Control.
Service Sheet BD2
8D-23
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