Scott 380R 390R Service Manual

Page 1

Scott 380R.390R

H. H. SCOTT, INC.

ADJUSTMENT

Equipment Required
Audio signal generator.

Level meter.
Oscilloscope.

Digital frequency counter, 0 - 100 kHz.
FM multiplex signal generator.

Circuit tester.

FM RF Tracking (PSTU031COX)

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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 sine wave. 1f failed, adjust T5.

4) Adjust 'll through T4 for maximum level meter reading
(Connected in parallel with the scope)

FM 1F Amplifier (PSTU041COX)

5) Adjust the signal generator for 106 MHz, and retune the
unit. Adjust CTS to tune in.

6) Adjust CT], CTZ, CT4 and CT6 for maximum level meter
reading,

7) Repeat above procedure again unril no further improve-
ment is obtained.

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1) Mute the FM local oscillator by shorting CV8,
2) Apply 10.7 MHz signal from the sweep generator to T3 in
the manner shown as above.

Oscilloscope

3) Adjust T6 and T7 for correct figure as provided below, It
may be necessary to increase or decrease the sweep gener-
ator output for adjustment convenience.

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Page 2

Pilot Signal (76 kHz) (PSTU032COX - 380R/PSTU038COX - 390R)

1) Apply 98 MHz, 65 dBf signal to the unit with no modu-
lation.
2) Adjust RV4 for 76 kHz 2200 Hz reading on the frequency

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 digital voltmeter to the right channel speaker
output terminal.

3) Adjust RVS for minimum leakage (minimum level) on the
voltmeter.

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 MHz, 65 dBf, 1 kHz and 100% modulated signal
to the unit, using same manner as in the FM Front-End
set-up.

Signal Strength Meter
1) Apply 98 MHI, 90 dBf signal to the unit.
2) Tune the unit to 98 MHz.

FM Mute Circuit
1) Apply 98 MHz. 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 T4 for maximum and symmetrical scope display as
shown below.

AM Tracking

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counter connected between T? (test point) and chassis
ground. The deviation within 2200 Hz is acceptable.

4) Apply 98 MHz, 65 dBf right channel composite signal to
the unit modulated same as step 1).

5) Move digital voltmeter to the left channel speaker output
terminal.

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 T1.

2) Adjust T2 for minimum distortion on the distortion ana-
lyzer, Readjust T1 if necessary. as turning T2 core may
upset the center-tuning meter balance.

3) Adjust RV2 for about 90% reading on the signal-strength
meter.

3) Place the Mute switch in on.
4) Adjust RVl, turning slowly until the signal is muted.

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