Scott 370R Service Manual
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Page 1
Scott 370R
ADJUSTMENT
Equipment Required
Audio signal generator.
Level meter.
Oscilloscope.
Digital frequency counter, 0-100 kHz.
FM multiplex signal generator,
Circuit tester.
FM RF Tracking
7
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F M SIgnal Generator Dumm y FM SPKR L eve] Me (er Oscilloscnne
An 1. AN 7 CU TPU T
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Analyzer 0 O
1) Apply 90 MHz. 1 kHz and 100% modulated, 65 dBf signal
with 76 kHz deviation to the FM antenna terminal,
2) Tune the unit to 90 MHZ.
3) Observe the oscilloscope connected to the Speaker output
terminal for synmetrical sme wave. If failed, adjust T4.
4) Adjust T1 through T3 for maximum level meter reading
(connected in parallel with the scope). '
FM IF Amplifier
T3
008:
00
Sweep Gnneramr
1) Mute the FM local oscillator by shorting CV7.
2) Apply 10,7 MHz signal from the sweep generator to T3 in
the manner shown as above.
To LhJSSVS
5) Adjust the signal generator for 106 MHZ, and retune the
uan.
6) Repeat 3), adjusting CT7, if necessary.
7) Adjust CT). CT3 and (ITS for maximum level meter
reading,
8) Repeat above procedure again untIl no further improve-
ment is obtained,
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3) Adjust T5 and T6 for correct figure as provided below.
It may be necessary to increase or decrease the sweep
generator output for adjustment convenience,
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Page 2
Pilot Signal (76 kHz)
1) Apply 98 MHz. 65 dBf signal to the unit with no modu-
lation.
2) Adjust RV4 for 76 kHz reading on the frequency counter
Stereo Separation
1) Apply 98 MHz. 65 dBf left channel composite signal to the
unit modulated with 1 kHz. 9% pilot signal with 6.75 kHz
deviation.
2) Connect a level meter to the right channel speaker output
terminal.
3) Adjust RVS for minimum leakage (minimum level) on the
meter.
FM Center-Tuning Meter
1) Remove the signal generator output from the unit.
2) With no signal supplied to the unit. verify that the FM
FM Distortion
1) Apply 98 Mill, 65 dBf, 1 kill and 100% modulated signal
to the unit, using same manner as in the FM RF tracking
set-up.
Signal Strength Meter
l) Apply 98 MHz. 90 dBf signal to the unit,
2) Tune the unit to 98 MHz.
3) Adjust RV2 for about 90% reading on the signal-strength
FM Mute Circuit
l) Apply 98 Mllz, 20 dBf signal to the unit,
2) Tune the unit to 98 MHz.
AM IF Amplifier
1) Apply 455 kHz sweep generator output to the unit's
AM Antenna terminal. '
2) Connect the scope to the pin No. 12 of ICS and the chassis
ground.
3) Adjust lll for maximum and symmetrical scope display
as shown to the right.
AM RF Tracking
1) Apply 600 kllz. 30% modulated with l kllz to the AM bar
antenna, as illustrated in next page. (Distance between the
AM bar antenna and emitting loop should be about 2 feet).
2) Adjust the signal generator output so that a sine wave
connected between T? (test point) and chassis ground.
Deviation within 1200 Hz is acceptable.
4) Apply 98 MHz. 65 dBf right channel composite signal to
the unit. modulated same as step 1).
5) Move level meter to the left channel speaker output ter-
minal.
6) Observe the right channel leakage appeared on the left
channel output. If necessary, readjust RVS for equal and
minimum level at both channels.
Center-tuning meter reads exact center of the scale. If
necessary. adjust T7.
2) Adjust T8 for minimum distortion on the distortion analyz-
er. Readjust T7 if necessary, as turning T8 core may upset
the center-tuning meter balance.
mEtetr
4) Perform this step in AM mode. applying LOOO kHz.
3) Place the Mute switch in On position.
4) Adjust RVl, turning slowly until the signal is muted.
appears on the scope.
3) Adjust T12 for maximum audio output on the level meter
connected parallel with the scope. when turning the
core, the audio level might rapidly increase and the volt-