Sharp R-961 (W) - Page 20

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
Isolate
the
high
voltage
rectifier
assembly
from
the
HV
circuit.
The
asymmetric
rectifier
can
be
tested
using
an
ohmmeter
set
to
its
highest
range
across
the
terminals
A+B
of
the
asymmetric
rectifier
and
note
the
reading
obtained.
Reverse
the
meter
leads
and
note
this
second
reading.
Ifan
open
circuit
is
indicated
in
both
directions
then
the
asymmetric
rectifier
is
good.
If
the
asymmetric
rectifier
is
shorted
in
either
direction,
then
the
asymmetric
rectifier
is
probably
faulty
and
must
be
replaced
with
high
voltage
rectifier.
When
the
asymmetric
rectifier
is
defective,
check
whether
magnetron,
high
voltage
rectifier,
high
voltage
wire
or
filament
winding
of
the
high
voltage
transformer
is
shorted.
CARRY OUT 4R CHECKS.
NOTE:
FOR
MEASUREMENT
OF
THE
RESISTANCE
OF
THE
RECTIFIER,
THE
BATTERIES
OF
THE
MEASURING
INSTRUMENT
MUST
HAVE
A
VOLTAGE
AT
LEAST
6
VOLTS,
BECAUSE
OTHERWISE
AN
INFINITE
RESISTANCE
MIGHT
BE
SHOWN
IN
BOTH
DIRECTIONS.
eee
D
HIGH
VOLTAGE
CAPACITOR
TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B.
Continuity
check
must
be
carried
out
with
measuring
instrument
which
is
set
to
the
highest
resistance
range.
.
Anormal
capacitor
shows
continuity
for
a
short
time
(kick)
and
then
a
resistance
of
about
10M@Q
after
it
has been
charged.
. Ashort-circuited capacitor shows continuity all the time.
.
An
open
capacitor
constantly
shows
a
resistance
about
10
MQ
because
of
its
internal
10MQ
resistance.
F,
When
the
internal
wire
is
opened
in
the
high
voltage
capacitor
shows
an
infinite
resistance.
G.
The
resistance
across
all
the
terminals
and
the
chassis
must
be
infinite
when
the
capacitor
is
normal.
If
incorrect
reading
are
obtained,
the
high
voltage
capacitor
must
be
replaced.
mo oO
CARRY OUT 4R CHECKS.
E SWITCH TEST
CARRY OUT 3D CHECKS.
Isolate
the
switch
to
be
tested
and
using
an
ohmmeter
check
between
the
terminals
as
described
in
the
following table.
Table: Terminal Connection of Switch
COM;
Common
terminal,
NO;
Normally
open
terminal
NC;
Normally
closed
terminal
S.C.;
Short
circuit,
O.C.;
Open
circuit
If
incorrect
readings
are
obtained,
make
the
necessary
switch
adjustment
or
replace
the
switch.
CARRY OUT 4R CHECKS.
R-961 - 18