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Model 8901B
Service
FM
DE-EMPHASIS
(PSI
25
50
75
750*
5 . Set the synthesizer frequency to 300 Hz. Set HP FILTER to 300 Hz. The waveform should have
an ac amplitude of 1.3 to 1.7 Vpp. If faulty, see Service Sheet 13 and check the 300 Hz High-Pass
Filter.
Waveform Amplitude Limits (Vpp)
Minimum
Maximum
1 . 3
1.7
1.3
1.7
1.3
1.7
1 . 3
1.7
6. Set the synthesizer frequency to 50 Hz. Set HP FILTER to 50 Hz. The waveform should have
an ac amplitude of 1.3 to 1.7 Vpp. If faulty, see Service Sheet 13 and check the 50 Hz High-Pass
Filter.
7.
Set the synthesizer frequency to 3 kHz. Set H P FILTER off and the LP FILTER to 3 kHz. The
waveform should have an ac amplitude of 1.2 to 1.8 Vpp. If faulty, see Service Sheet 13 and check
the 3 kHz Low-Pass Filter.
8. Set the L P FILTER
off and FM DE-EMPHASIS to PRE-DISPLAY. Set the synthesizer
frequency and FM DE-EMPHASIS as listed in Table 8D-13. For each setting, the ac amplitude
of the waveform should be as indicated. If faulty, see Service Sheet 13 and check the appropriate
de-emphasis filter.
lbble 80-13.
Amplitude at A3TP3,
@
Step 8
Synthesizer
Frequency
6366
31 83
2 1 22
2 1 2 . 2
(Hz)
~
~~
Kev in
2.3
9. Key in 2.2 SPCL. Switch PRE-DISPLAY off. The waveform should have an ac amplitude of 1.9
to 2.3 Vpp. If faulty, see Service Sheet 13 and check the Pre-Display Switching.
10. Set the synthesizer frequency to 1 kHz. Press
@M. The waveform should have an ac amplitude
of 1.9 to 2.3 Vpp. If faulty, see Service Sheet 13 and check the Phase Modulation Integrator.
11.
Press PEAK-. The waveform should not noticeably change amplitude. If faulty, see Service Sheet
13 and check the Inverting/Non-Inverting Amplifier.
12. Press FM. Switch off all FM DE-EMPHASIS. Connect the oscilloscope to MODULATION
OUTPUT/AUDIO INPUT. The waveform should have an ac amplitude of 1.9 to 2.3 Vpp. If
faulty, see Service Sheet 13 and check the Output Amplifiers.
13. Key in 49.6 SPCL. This causes the output of the audio range detector to be displayed. The display
should read 0.4 to 0.6. If faulty, see Service Sheet 13 and check the Absolute Peak Detector.
14. Key in 0.15 SPCL. The display now shows the audio overvoltage status. The display should read
000000.0000. If faulty, see Service Sheet 13 and check the Audio Overvoltage Detector.
15. Increase the synthesizer level to +10 dE3m. The display should read 000001.0000 indicating that an
audio overload has been detected. If faulty, see Service Sheet 13 and check the Audio Overvoltage
Detector.
NOTE
To repeat steps 13 and
14,
it
i s necessary to press CLEAR first to clear the
audio overvoltage latch.
8D-42
Service Sheet BD4
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