Model 8901B Service
6.
7.
8.
9.
10.
11.
NOTE
This is not a valid measurement of the filter bandwidth since the
source
impedance
is
incorrect. It will, however, show up a severe problem.
For
a more precise test of bandwidth, see Service Sheet
12
or
perform
Performance Test 4-Audio Filters
in Section
4.
Set the synthesizer level to -27 dBm and frequency to
1
kHz. Connect
its
output
to
A2J2 (FM
IN). Press FM. The waveform should have an ac amplitude of
3.0
to
3.6 Vpp. If faulty, see Service
Sheet 12 and check the 260 kHz Low-Pass Filter at the FM output.
Increase the synthesizer frequency to 260 kHz. The waveform should have an ac amplitude of
1.1
to
1.5 Vpp. If faulty, see Service Sheet 12
and
check the 260 kHz Low-Pass Filter at the
FM
output.
NOTE
This is not a valid measurement
of
the filter bandwidth since the source
impedance is incorrect. It will, however, show up a severe problem.
For
a more precise test of bandwidth, see Service Sheet
12
or
perform
Performance Test 4-Audio Filters
in Section
4.
Set the synthesizer level to -17 dBm and frequency to
1
kHz. Key
in
2.2 SPCL to reduce the
audio gain by 20
dB.
The waveform should have an ac amplitude of 950 to 1150 mVpp. If faulty,
see Service Sheet 12 and check 20
dB
Attenuator
1.
Key in 2.3 SPCL to reduce the audio gain another 20
dB.
The waveform should have an ac
amplitude of 95 to 115 mVpp.
If
faulty, see Service Sheet 12 and check 20
dB
Attenuator 2.
Key in 2.2 SPCL. Set the synthesizer frequency to 110 kHz. Set
LP
FILTER to >20
kHz.
The
waveform should have an ac amplitude of 400 to 600 mVpp.
If
faulty, see Service Sheet
12
and
check the >20 kHz Low-Pass Filter.
Set the synthesizer frequency to 15 kHz. Set LP FILTER
to
15
kHz. The waveform should have
an amplitude of 600 to
900
mVpp.
If
faulty, see Service Sheet 12 and check the 15 kHz Low-Pass
Filter.
(J2)
Audio Filters and De-emphasis Check
NOTE
This check assumes that
a
Audio Filters and Gain Check
gives positive
results.
1.
2.
3.
4.
Set the audio synthesizer to
1
kHz at -17 dBm. (The synthesizer output impedance should be
500.)
Connect
its
output to A2J2 (FM IN).
Connect a high-impedance, ac coupled oscilloscope (with
1O:l
divider probe) to A3TP3 (DE-EM
OUT).
Set the signal generator to approximately 20
MHz
CW
at
0
am. Connect its RF output to the
Modulation Analyzer’s INPUT.
Press the blue key, then press INSTR PRESET (the AUTOMATIC OPERATION key) to preset
the instrument. Press FM. Key in 2.2 SPCL to set the audio gain
to
an intermediate range. The
oscilloscope should show a sinusoidal waveform with an ac amplitude of 1.9 to 2.3 Vpp.
If
faulty,
see Service Sheet
13
and check the audio path beginning at the high-pass filters.
Service Sheet
BD4
8D-41
To Next Page
Loading...
