Kenwood KA-7002, Руководство по обслуживанию

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