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DIFFERENTIAL AMPLIFICATION STAGE
Replacing the differential stage transistors (Oq
•
should replace both the same characteristic transis
tors.
1.
Connect the dummy load
output terminal.
2.
Check the voltage across the dummy by using the
tester or DC VTVM.
3.
Adjust the
variable resistor (VRq
*
meter indicates within
Don't touch the variable resistor without neces
*
sity.
IDLING CURRENT
Center voltage adjusting variable resistor (VRq
•
main unit is not turned without adjusting differential
amplification stage.
1.
Connect the dummy load
output terminal.
2.
Connect the audio generator to the MAIN-IN jack.
Oscilloscope and AC VTVM are connected across the
dummy.
3 .
1
Feed the
kHz signal to the set.
4. Before checking the idling current, turn on power
switch in a few minutes, adjust the variable resistor
3.4)
(VRq
so that tester (or DC VTVM) coupling to
the collector of transistors indicates
At the same time check the waveform to be correct
3).
(Fig.
Not getting the correct waveform on oscilloscope,
check the
collector
Because transistor of other channel is broken down.
LOUDSPEAKER PROTECTION CIRCUIT
By some reasons, output terminal is shorted or final
0 1
4)
transistors (
�
protects the loudspeaker from damage.
the sound, check the center voltage (see the differential
amplifier stage).
It is good that hand of meter indicates
0
± 1OOm V.
If it does more than that, check the tran
sistors in final or drive stage.
without abnormality, it is causes that transistor
poor. Check and replace it. Do the transistor
8
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ALIGNMENT PROCEDURE
(8n, 80
watts) to the
1,2)
so that the
0
100
1)
±
mV.
(Fig.
(8n, 80
watts) to the
50
mA (Fig.
current of each transistors.
is breakdown, then relay works and
Not listening
Protection circuit works
(06)
1
8).
�
1.2)
in
2).
I
I
I
I
(021
I
01
(05)
is
also.
A.
I
I
Fig. 1 Check the center voltage
Fig. 2 Adjust the idling
D
I
\
'
I
\
'
'
i
I
\
.
\
Fig. 3 Best wave form
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