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Service
Model 8901B
4. Readjust the level from the synthesizer for a display of 3 Vpp. Key in 30.0 SPCL to set the
instrument to measure External Audio RMS Level. The 1 kHz signal should disappear. If faulty,
see Service Sheet 16 and check the Internal/External Source Switch.
5. Connect the oscilloscope to A52TP4 (BUF OUT). Connect the synthesizer to the MODULATION
OUTPUT/AUDIO
INPUT.
The
1
kHz audio signal should be displayed with an amplitude
between 2.8 and 3.2 Vpp. If faulty, see Service Sheet 16 and check the Audio Input Buffer.
6. Connect the oscilloscope to A52TP2 (AMPL
1
OUT). Key in 2.3 SPCL to assure that the 20
dB
attenuator of Amplifier 1 is in. The amplitude of the displayed audio signal should be between 2.8
and 3.2 Vpp. If faulty, see Service Sheet 16 and check Amplifier 1 and the Notch Select Switch.
7. Reduce the amplitude
of the signal from the synthesizer by 10 (that is, -20
dB).
Key in 2.4 SPCL
to bypass the 20
dB
attenuator. The amplitude of the displayed audio signal should be between
2.8 and 3.2 Vpp. If faulty, see Service Sheet 16 and check Amplifier
1.
8. DC couple the oscilloscope and connect it to A52TP1
(RMS
OUT). The oscilloscope should
display a voltage between 0.9 and 1.2 Vdc. If faulty, see Service Sheet 16 and check the RMS-to-DC
Converter and the Ripple Filter.
9. AC couple the oscilloscope and connect it to A52TP3 (NOTCH FLTR OUT). Key in 0.2 S (Shift)
0 S 4 SPCL to keep the Notch Select Switch in the through position, keep the gain of Amplifier
1 at 20
dB,
switch in the 400 Hz Notch Filter, and
set
the gain of Amplifier 2 to 20
dB.
The
amplitude of the displayed audio signal should be between 2.7 and 3.3 Vpp. If faulty, see Service
Sheet 16 and check the Notch Filters and Amplifier 2.
10. Key in 0.2
S 0 S 0
SPCL to reduce the gain of Amplifier 2 by 20
d B .
The amplitude of the
displayed audio signal should be between 270 and 330 mVpp. If faulty, see Service Sheet 16 and
check Amplifier 2.
11. Key in 0.2 S 0 6 SPCL to switch in the 1 kHz Notch Filter and increase the gain of Amplifier 2
by 20
dB.
The
1
kHz audio signal should disappear into the noise.
If
faulty, see Service Sheet 16
and check the Notch Filter.
12. Set the synthesizer frequency to 400
Hz. Key in 0.2
S 0 S 4 SPCL to insert the 400
Hz Notch
Filter. The 400 Hz audio signal should disappear into the noise. If faulty, see Service Sheet 16
and check the Notch Filter.
13. Connect the oscilloscope again to A52TP2. Key in 0.2 S 0 7 SPCL to set the Notch Filter to 1
kHz, keep the gain of Amplifier 2 at 20
dB,
set the gain of Amplifier 1 to 0
dB,
and set the Notch
Select Switch to the notch filter position. The 400
H z
audio signal should have an amplitude
between 2.7 and 3.3 Vpp. If faulty, see Service Sheet 17 and check the Notch Select Switch.
(J7) Audio
Counter
Check
1.
Set the audio synthesizer to
1
kHz at 1 Vrms (into a high impedance). Connect its output to the
2. Connect an ac coupled, high-impedance oscilloscope to A52TP4 (BUF OUT).
3. Press the blue key, then press INSTR PRESET (the AUTOMATIC OPERATION key) to preset
the instrument. Press S (Shift) AUDIO FREQ. Press AUDIO INPUT. The
1
kHz audio signal
should be displayed on the oscilloscope with an amplitude between 2.6 and 3.0 Vpp. If faulty,
perform
0.
MODULATION OUTPUT/AUDIO INPUT.
8D-44
Service Sheet BD4
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