Eddystone 990R - Power Supply; General; Fusing and Protection

POWER SUPPLY
General
.
This part of
the
receiver is
of
conventional
design
and allows
operation
from
any
standard AC supply or
12V DC.
AC
Operation
.
In the case
of
AC
working,
a
full-wave selenium low-voltage
bridge
rectifier
is
fed
from
the
low-voltage
secondary
-winding
(
14
V)
on
TI
4
. Tappings
are
provided
on
the
split primary
windings
to allow
adjustment
for the
local mains
voltage. Zener
diode
D13
(0AZ23O)
regulates
the
output
from the
rectifier at
12V
to feed
the
high-level
audio stages
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?
OV
ze^or
circle *
DC Operation .
For
DC
working,
the
shorting
plug
(PL8)
is
removed from
SK
13
to
isolate
the
12V
zener
diode and
the
AC
transformer.
Connection of the external
12V supply
is then
by
PL9,
the
10V line
being
regulated
in the
normal manner
by
the 0AZ228.
Fusing and
Protection .
FS1
fuses
the
negative
12V
supply
line and
is
wired to
be
in circuit
for
both
DC
and
AC
operation.
On
AC, an
additional
fuse (FS2)
is
included
in the
live
line to
the
power
transformer
primary.
Switching
is
by S10A and
SlOB
which
interrupt
both the AC
and
DC
circuits
in the
"off"
position. S10 is ganged
to the
MODE
SWITCH S7*
A silicon
diode
(D12 s
DD006)
is
wired directly
across
the 12V
input and serves
as
a
protection
device
in
the event
of
the
supply
being connected
with
reversed polarity.
If this
occurs,
D12
conducts
in
a
forward direction and draws a current
which exceeds
the
rating
of
FS1.
The fuse fails
and
isolates the receiver from the
supply.
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11
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