Werbung
HITACHI HMA.6500
o
Removing
the printed wiring
boards
o
Ausbau
der Leitterplatten
o
Déposer
des
plaquettes
à
circuit
imprimé
Powen
supply
(A
3q6Dr
O
^
Stromqúíb t
úeor
(O
Alimentoîion
3 I
I
frloin
omp @
Houptversîórker
SERVICE
POINTS
o
As this
unit
uses
a
large
capacity power supply,
be
careful
of
the
following points when
checking
and
repairing.
(1)
To
check and repair the
printed
wiring
boards, bé
sure
to
cut
off
the
power
and
pull
out the power
cord.
Discharge
the
power
capacitors
by
touching
it
with
a
resistor
of
approx.
10 ohms,
5
watts
capacity
at
the
positions C803 and C804.
When
discharging
through
the
chassis
ground,
there is
danger
that
Rl
or R2
may
be open and noise
becomes
mixed,
in
this
case,
so
be
sure
to
discharge between
the
@ andQ
terminals
of
the
electrolytic
capacitor.
(2)
Do
not
touch
the terminals
of
nearby parts
with
a
DC
voltmeter
when
connecting
it
for
adjusting
the
idle
current
as
malfunction
may
result.
Handle the DC
volt-
meter carefully. Wind insulating
tape around
the
screw-
driver.
.
Parts
installation method
Great care
is
taken in
installing
parts
to
improve
the
safety
of
products.
For
example,
parts
are covered
with
tubes,
or
they
are
kept
away
from
the printed wiring
board
surface.
Be
sure
to
maintain
the
previous
condi
tions after
replacing parts
for
repair.
.
DIRECT COUPLING/CONDENSER COUPLING switch
Since
this
is
a
DC amplifier, when direct current
leakage
occurs
in
equipment connected
to
the
input,
it
will
be
amplified
and
a
DC
bias
is
placed
to the
speaker causing
deterioration
of
tone
quality
and generation
of
distor-
Amplif
icoteur
principo
I
Fig.
3
Abb.3
tion
:
this switch
prevents this.
This
al.so
prevents
the flow of
a
large
DC
component
because
of
trouble
in
the control
amplifier which
would
damage
the
speaker.
If
there
if
DC
leakage
in
the
input,
a
noise
("puu ...")
is
heard
when turning this
switch,
so
change
to
CONDENSER
COUPLING at that time.
oRl
The
ground
of
the
signal
line
and the
chassis
ground
of
the unit
are
connected using
Rl
(47
ohms)
as shown
in Fig.
4.
c
round
orR
lr.
v>
Chassis
ground
Fig.4
The
is
because
the
POWER
MOS
FET
is
in
the
source
case,
and
in
order to maintain the
capacity between
FET
and
the
radiation fan,
stability
deteriorates
by
this,
so
the FET is
isolated
from
the
chassis
using a
resistor
of
47
ohms.
Accordingly,
be careful
not to
cause
an
output by
touch-
ing
the
Q
lead
wire
of
the
speaker
to
the
chassis
or
dis-
charge
the electrolytic
capacitor
during
servicing,
since
this may
cut
the
lead
wire of
Rl
or R2
and introduce
nolse.
5q
î.
î
î
'Woshcr
_kl)
@
-4-
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