Pioneer PX-7 Service Manual page 124

13.
23 Power Supply
Circuit
The PX-7 power
supply circuit
consists of a
primary
coil line
filter,
a
power
transformer
(Tl),
and secondary
coil
rectifier,
and
a
number
of
regulators to obtain
+5V
(Vccl),
+12V
(Vcc2),
and
-12V (Vcc3).
The
primary
coil
voltage
can be switched to
220V
and
240V
to
enable the
PX-7
to
be used
in
different
regions.
Inserting the
Tl
primary
coil
cable
connector
in
J24
sets
the voltage to
240V,
while inserting in
J25
sets
the voltage to
220V.
HB
models have been
set
to
240V
and
HE
models
to
220V
prior to
shipment from
the factory. If
for
some
reason, however, the voltage setting
needs
to
be changed,
it
will
be necessary to
open
the
bonnet
and reconnect the
connector
described
above
(user
servicing
not permitted).
While the
HB
model
power
cable
has not
been
fitted
with
a plug,
HE
model
has
been
fitted
with
the
European
(conti-
nental) plug.
The
line
filter
consisting
of L105,
C414, C415, C416, C418, C419, and
C420
reduces
power
line
noise for
improved operational
stability.
D127
is
the
power
indicator
LED
(red),
and
D133
diode
is
inserted to
prevent back
current.
The
+5V
and
+12V
power
lines
are regulated
by
bridge diode
D125
and D126,
triode regulator
IC115
and IC114.
The
—12V
line
is
regulated
in
conformity with
the
+12V
line.
IC115 and IC114
include L-shaped
current
limiters for protection
against overcurrent.
And
R418
and Q406
are
used
for overcurrent protec-
tion
purposes
in
the
—12V
line.
Note
that the +5V,
+12V, and
—
12V
lines are
all
opened
externally
via
the various input/output connectors
to prevent
damage by
possible
short shorting as a
result
of
user misoperation.
ICIM<|iP078l2H)
SO/60HZ
Fig.
13-64
Power
supply
circuit