Model
8901B
Service
NOTE
A
slight fuzziness on the wweform is normal. It
is
the doubled
1.5
MHz IF
carrier.
6. Connect the oscilloscope
to
A4TP5 (FM OUT). The waveform should be 3.6
to
4.4 Vpp.
If
faulty,
see Service Sheet
11
and check the FM Output Amplifier and Squelch.
NOTE
This wweform will have even more
of
the doubled
1.5
MHz carrier on
it.
@
FM
Calibrator Check
1.
Connect a high-impedance, ac coupled oscilloscope (with
1O:l
divider probe) to A51TP2
(TRAPEZOID OUT).
2.
Press FM and CALIBRATE. The waveform should be trapezoidal with round edges and an ac
amplitude of
300
to
340 mVpp and period of 90
to
110
ps.
(Ignore
Error 08
in the display.) If
faulty, see Service Sheet 29 and check
the
trapezoid generation circuits.
3.
Key
in
12.1
SPCL and 46.3 SPCL. This sets the FM Calibrator to CW and causes the display
to
show
its
frequency. The display should read between 1009000 and 1011000.
If
only slightly out of
limits, perform the
Adjustment 9-FM Calibrator
in Section
5.
Otherwise, see Service Sheet 29
and check the
10.1
MHz VCO.
4. Key in 12.0 SPCL. This causes the display to read the computed peak deviation. The display
should read between
31
and 37 kHz.
If
only slightly out
of
limits, perform
Adjustment 9-FM
Calibrator.
Otherwise, see Service Sheet 29 and check the 10.1 MHz VCO.
5. Key in 12.1 SPCL. Connect the ac coupled oscilloscope to the CALIBRATION AMFM
OUTPUT. Switch the input impedance
of
the oscilloscope
to
500
or
terminate the input in
500
using a tee. The waveform should be approximately sinusoidal and have an ac amplitude of 35 to
45 mVpp.
If
faulty, see Service Sheet 29
and
check the Output Amplifier.
If
it
is
good, see Service
Sheet 30 and check the RF path through the AM Calibrator.
AM
Calibrator Check
1.
Connect an ac coupled oscilloscope to the CALIBRATION AMFM OUTPUT. Switch the input
impedance of the oscilloscope to 500
or
terminate the input in
50R
using a tee.
2. Key in 13.1 SPCL to set the AM Calibrator to CW. The waveform should be approximately
sinusoidal with an ac amplitude of 35 to 45 mVpp. If faulty, see Service Sheet 30 and check the
RF path beginning at the input
of
the FM Calibrator.
3.
Key in 13.0. This causes the display to show the AM depth. The display should show between
33.0 and 33.7%.
If
faulty, see Service Sheet 30 and begin by checking the Modulators.
4. Press AM then CALIBRATE. The waveform should show the carrier with AM. The AM envelope
should be a rounded squarewave with a period of 90 to 110
ps.
The amplitude of the peak should
be twice that
of
the trough. If faulty, see Service Sheet 30 and check the
10
kHz Modulation
Oscillator.
Service Sheet BD3 BD-31
To Next Page
Loading...
