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.
Precautions on
troubleshooting and
replacing parts
(1)
When
the
stabilized
power
circuit
and
the
peripheral
parts
of
Q701
and Q702
(D106, R752, R753
and
their
peripheral parts)
are replaced,
the
adjustment
of
the
input/output DC
may
drift,
so
be
sure
to
check
the
input/output/
DC voltage.
(2)
Since
@
grade
of hrs is
specially
classified into
@ - @fo.
Q701
and
Q702,
replace
them
match-
ing the
proper
grade
with
the proper
channel.
(3)
Since
the
socket
for
transistor
use
is
used
for
the
socket
of
the
POWER
MOS
FET, polarity
is indicated
as
B, C, E. Match
it
to
the
indications
shown
in
Fig.
5
when
replacing
the
POWER
MOS FET
and
when
checking.
.
Gautions on checking
the
voltage
(1)
Oscillations
may occur
depending
on the
voltmeter
HITACHI HMA-6500
used
when
checking
the
gate
voltage
at FET
701
L/R.
If
this
happens, measure
the
collector voltage of
Q704
LiR
as
it
is at the
same
potential
as
FET
701
L/R.
The
protection circuit may
operate
when
checking the
collector voltage
of
Q706
L/R
and the
base
voltage
of
Q707
L/R.
In
this
case, change
the
measurement
position
and
measure
the
voltage between
the
respective electrodes.
Gate
(G)
Fig.
5
(2)
ADJUSTMENT
.
Adjusting
idle
current
Perform adjustment
with
no
signal
and
with
the
speaker
switch turned OFF.
Remove
the wiring
@
, @
shown
in
Fig.
6 and connect
the
@
side
of
the
DC
ammeter
to
the drain
side
of
the
FET and
the O
side
to
the
main amp.
PWB.
Next,adjust
R75
lL
and
R75
lR
on
the
main
amp.
PWB.
so
that
they
are
both
150mA.
Attached
the
wiring
@
,
@
as
they
were,
after
adjust-
ment
is completed.
IEI|OZR
FETTOZL
Fig.6
o
Adjusting the
input
DC
Insert the
shorting
pin to
the input,
set
the
DIRECT
COUPLING/CONDENSER COUPLING
switch
to
CONDENSER COUPLING,
turn the
speaker
selector switch
ON, and
turn
the
powet
switch
ON
with
no
load
for
more than about
8
minutes
before
performing the
adjustment.
To
adjust
Lch,
connect
the@
side
of
the DC
arnmeter
to 13
terminal
of
the
main
amp. PWB,
and
the
Q
side
to
14
terminal.
To
adjust
the Rch, connect
the
@
side
to l5
terminal,
and
the
Q
side
to
14
terminal. Then perform the
adjust-
ment
using
R152L
or
R752R
respectively
for
a
zero
reading
(within
t
0.5V) with
the 3mV
range.
(Fig.
7)
o
Adjusting the
output
DC
Be
sure
to
perform
this
adjustment
after
the
input
DC
adjustment
is
completed.
Insert the
shorting
pin
in
the input,
set
the
DIRECT
COUPLING/CONDENSER
COUPLING switch
to
CONDENSER
COUPLING, turn the
speaker selector
switch ON,
and
perform the
adjustment
with
no load.
Fig.7
Perform
adjustment using
R753L or
R753R
after
con-
necting the DC ammeter
to
the
@
and
Q
sides
of
the
speaker
A
terminals
of
Lch
or Rch
for
a
zero
reading
(within
+5mV),
with
the
l00mV
range.
(Fig.
7)
Adjusting the
meter
Adjusting the
meter
sensitivity
Adjust
sensitivity
of
the
meter
after
zero
adjustment
is
completed.
With no
load
applied
to
the
speaker ter-
minals, connect
the
audio oscillator
to
the
input
terminal (INPUT)
to
feed
in
a
signal
of lkHz.
In
this
case,
adjust
the input
so
that
the
Lch
pointer
indicates
1W.
Then adjust R955R so that the Rch pointer
also
indicates
lW
(Fig.
7).
o
(1)
FETT02R
Fig. 6
-5-
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