Adjustments - Yamaha YST-SW800 Service Manual

YST-SW800

ADJUSTMENTS

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 A and B
in the schematic diagram according to the following
procedure.
Devices required
Signal generator (100Hz sine wave)
8Ω or 6Ω load resistor
Oscilloscope (dual trace type)
Connection
1) Connect the output signal from the signal generator
to the input terminal of YST-SW800.
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
minimum output level settings.
2) Set the volume of YST-SW800 to the minimum
position.
3) Turn on the power to YST-SW800.
4) Adjust the output level of the signal generator and the
volume of YST-SW800 so that the output level
observed at oscilloscope CH2 is 70Vp-p.
Waveform observation
With the settings made as described above, observe
the waveform obtained at CH1 for judgment.
Normal
Point A (Cathode of D27)
V : 50V/div H : 2 msec/div
DC range 1 : 1 probe
0V
Point B (Anode of D24)
V : 50V/div H : 2 msec/div
DC range 1 : 1 probe
0V
7
Idling Adjustment
To stabilize operation of the amplifier, turn ON the
power with no input signal and wait for 1 or 2 minutes
in non loaded condition before the adjustment.
Adjust VR1 so that the voltage between terminals
TP1 and TP2 is DC 50mV to 250mV.
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 R162
on the MAIN (2) P.C.B.
3) Connect the output signal from the signal generator
to the L/MONO terminal of YST-SW800.
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.
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.
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.
Abnormal
+B or GND level
After confirmation
Becomes constant
1) Turn off the power switch.
2) Disconnect the 10kΩ resistor connected to both ends
of R162.
Abnormal
-B or GND level
Becomes constant