Service manual
Table Of Contents
SAFETY
PRECAUTIONS
(Continued)
8.
ISOLATION CHECK (SAFETY
FOR
ELECTRICAL SHOCK HAZARD)
After
re-assembling
the
product,
always
perfrom
an
isolation check on
the
exposed metal parts
of
the cabinet, screwheads, cable jacks, controls shafts, etc.,
to
be
sure
the
product
is safe
to
operate
without
danger
of
electrical shock.
(A)
DIELECTRIC STRENGTH TEST
The isolation between
the
AC primary
circuit
and all metal parts exposed
to
the
user, par-
ticularly any exposed metal part having a return path
to
the chassis should withstand a voltage
of
1,
100V
AC (r.m.s.)
for
a period
of
one second.
This method
of
test
requires
test
equipment
not
generally found in
the
service trade. *
(8)
LEAKAGE CURRENT CHECK
*
Plug
the
AC
line cord
directly
into
the
AC
outlet
(do
not
use a line isolation transformer dur-
ing
this
check). Using a
"Leakage
Current
Tester",
measure
the
leakage current
from
each
exposed metal part
of
the
cabinet, particularly any exposed metal part having a return path
to
the
chassis,
to
a
known
good earth ground (water pipe, etc.).
Any
leakage current
must
not
exceed
0.5mA.
ALTERNATE CHECK METHOD
Plug the AC line cord directly into
the
AC
output
(do
not
use a line isolation
transformer
during this check). Use
an
AC
voltmeter
having
1,000
ohms per
volt
or more
sensitivity
in
the
following
manner. Connect a
15000
10W
resistor paralleled by a 0.15JLF AC-type
capacitor between
an
exposed metal part and a
known
good earth ground (water pipe, etc.).
Measure
the
AC
voltage across the resistor
with
the
AC
voltmeter.
Move
the
resistor connection
to
each exposed metal part, particularly any exposed metal
part having a return path
to
the chassis, and measure
the
AC voltage across
the
resistor.
Now,
reverse the plug in the AC outlet and repeat each measurement.
Any
voltage measured
must
not
exceed
0.35V
AC (r.m.s). This corresponds
to
O.5mA AC (r.m.s.).
CAUTION:
When
troubleshooting,
with
power
applied, use an isolation
transformer
and
confirm
that
the
CRT
earth
wire
is
connected
to
the
CRT
socket
board
and
the
chassis.
3