Adjustments - Yamaha YST-SW205 Service Manual

YST-SW205/305
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I ADJUSTMENTS
G Confirmation of Power Amp operation
For the power amplifier which has been repaired, it is
absolutely necessary to confirm that a correct waveform
is obtained at points indicated by
schematic diagram according to the following procedure.
Devices required
Signal generator
8 Ω or 6 Ω load resistor
Oscilloscope (dual trace type)
Connection
1) Connect the output signal from the signal generator to the
input terminal of the unit.
2) Disconnect the connector terminal connected to the
speaker unit and reconnect it to the load resistor.
3) Connect the HOT side of the oscilloscope CH1 probe to
the point A or B indicated in the figure and the GND side
to the GND of the main unit.
4) Connect the oscilloscope CH2 input to the red side of the
connector cable, which is connected with the load
resistor.
At this time, the GND terminal of CH2 must be left
unconnected.
Setting
1) Set the signal generator to the sine wave, 100Hz and
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L 13942296513
minimum output level settings.
2) Set the volume of the unit to the minimum position.
3) Turn on the power to the unit.
4) Adjust the output level of the signal generator and the
volume of the unit so that the output level observed at
oscilloscope CH2 is 28Vp-p.
Waveform observation
With the settings made as described above, observe the
waveform obtained at CH1 for judgment.
Normal
Point A (Cathode of D29)
V : 20V/div H : 2 msec/div
DC range 1 : 1 probe
0V
Normal
Point B (Anode of D31)
www V : 20V/div H : 2 msec/div
DC range 1 : 1 probe
.
0V
7
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and B in the
A
Abnormal
+B or GND level
Becomes constant
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Abnormal
-B or GND level
Becomes constant
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G Idling Adjustment
To stabilize operation of the amplifier, turn ON the power
with no input signal and wait for 2 to 3 minutes in non loaded
condition before the adjustment.
Adjust VR1 so that the voltage between terminals TP11 and
TP12 is 30mV to 200mV.
G Confirmation of AUTO STANDBY operation
Setting
1) Turn off the power switch.
2) In order to shorten the time required for operation check;
connect a 10kΩ resistor at both ends of R60 on the MAIN
(3) P.C.B.
3) Connect the output signal from the signal generator to the
L/MONO terminal of the unit.
4) Set the signal generator for the sine wave of 100Hz,
8mV.
5) Turn on the power switch.
Confirmation
1) Set the AUTO STANDBY switch to the LOW position.
STANDBY
OFF
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2) Turn on the STANDBY/ON switch.
The display LED lights up (green) and its color changes
to red after 5 to 10 seconds.
3) Turn off the STANDBY/ON switch.
The display LED goes off.
4) Set the AUTO STANDBY switch to the HIGH position.
STANDBY
OFF
5) Turn on the STANDBY/ON switch.
The display LED lights up (green) and its color remains
unchanged even after time have elapsed.
6) Turn off the STANDBY/ON switch.
The display LED goes off.
After confirmation
1) Turn off the power switch.
2) Disconnect the 10kΩ resistor connected to both ends of
R60.
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AUTO
HIGH
LOW
0 5 8 2 9 9 4 2 8
AUTO
HIGH
LOW
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