not
lose
its
data
when
power
is
turned
o.
The
EEPROM
is
mounted
in
a
socket
for
easy
replacement.
Jumpers
and
switches
set
the
4339B
conditions
.
Refer
to
Appendix
B
for
more
information.
P
ower
Supply
Section
Figure
4-7
shows
the
P
ower
Supply
Section
block
diagram.
Figure
4-7.
P
ower
Supply
Section
Block
Diagram
The
ac
line
power
is
connected
to
the
A5
A
C
Inlet
Board
Assembly
,
which
consists
of
a
fuse
,
line
switch,
voltage
selection
switch,
and
the
varistors
.
The
voltage
selection
switch
selects
the
ac
line
voltage
either
230
V
or
115
V
.
A
ccording
to
the
selection,
the
ac
line
power
is
connected
to
the
corresponding
primary
tap
of
the
transformer
.
V
aristor
,
VR1
protects
the
circuit
from
surge
voltage
on
the
line
power
.
VR2
blows
the
fuse
F1,
if
the
4339B
is
turned
on
with
wrong
line
voltage
setting
selection,
for
example
,
115V
selection
when
using
230
V
line
voltage
.
Note
Because
very
high
dc
isolation
is
required
between
A3
Ammeter
assembly
and
the
other
assemblies
,
the
4339B
has
two
independent
dc
voltage
supply
systems
.
Both
of
the
transformer
secondary
voltages
are
approximately
14
V
.
One
of
the
ac
voltages
is
rectied
and
ltered
by
circuitry
on
the
A1
Main
Board
Assembly
,
and
produces
approximately
14
Vdc
.
The
dc
voltage
is
applied
to
the
DC-DC
Converter
to
produce
regulated
+5
V,
+
12
V,
and
012
Vdc
.
The
dc
voltages
are
supplied
to
all
the
assemblies
except
A3,
either
directly
or
indirectly
via
the
A1
assembly
.
The
other
ac
voltage
is
rectied
and
ltered
on
the
A3
Assembly
.
A
dc-dc
converter
on
the
A3
assembly
provides
regulated
+5
V,
+12
V,
and
012
Vdc
for
the
A3
assembly
operation.
T
roubleshooting
4-9
