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4. TEST
EQUIPMENT REQUIRED
FOR
SERVICING
This table lists the test equipment required for servicing the Model Sm-8 Stereo Power Amplifier.
Distortion Analyzer
Distortion measurements
Audio Oscillator
AC VTVM
Oscilloscope
Sinewave and squarewave signal source
Voltage measurements (AC)
Waveform analysis and trouble shooting and ASO alignment
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Circuit Tester
DC VTVM
Trouble shooting
Voltage measurements (DC)
AC Wattmeter
Line Voltmeter
Variable Autotransformer (0 ~ 140V AC, 10A)
Monitors primary power to amplifier
Monitors potential of primary power to amplifier
Adjust level of primery power to amplifier
Shorting Plug
5. ADJUSTMENT
PROCEDURES
1. Class B idting adjustment
a) Apply a sine wave signal of 1 to 2 VRMS to JL14
from an audio oscillator in order to forcibly make it
Operate as a class B amplifier.
b) Adjust
RL43 and RL44 so as to give DC voltage of
7 mV at the JJO1-02 and JJ03-04 test points.
NOTE:
Carry out the adjustment one minute after the
switch is turned on.
After the set is stabilized,
the voltage should be 27 mV (50 mA).
2. Class A idling adjustment
a) Disconnect the input to JL14.
b) Adjust
RL39 and RL40 so as to give DC voltage of
440 mV at the JJO1-02 and JJ03-04 test points.
NOTE:
Carry out the adjustment one minute after the
input to JL14 is disconnected.
The class B ad-
justment must be done first.
After the unit is
stabilized,
the
voltage
should
be
370 mV
(655 mA).
3. Comparator balance adjustment
a) Connect a trigger oscilloscope to JL14.
b) Set the load of the device to OPEN, apply a signal
with a frequency of 1 kHz and increase it gradually.
c) While observing the output waveform of the unit and
pulses
at JL14, adjust
RL31
so as to generate two
pulses per output waveform period.
Shorts amplifier input to eliminate noise pickup
rae
acs
Output waveform
+5V
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JL14 T.P
Ov
4. Switching level adjustment
a) Connect a trigger oscilloscope to JL14.
b) Set the load of the unit to OPEN and apply a signal
having a frequency of 1 kHz to the L channel.
c) With
the output set to 15.5V, adjust RLOQ so as to
generate pulses at JL14.
d) Apply a signal to the R channel and, similarly, adjust
RL10.
5. Power meter adjustment
a) Set the load of the unit to 8Q, apply a signal having
a frequency of 1 kHz and increase the input signal to
30.9V.
b) Adjust the following so as to give a reading of 120V
on the meter.
For the L channel, adjust R X05.
For the R channel, adjust RX06.
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