Advertisement
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
Advertisement
