SAFETY CHECK-OUT
(US Model only)
After
correcting
the
original
service
problem,
perform the following safety checks before releasing
the set to the customer:
l.
Check the area of your repair for unsoldered or
poorly-soldered connections.
Check
the entire
board surface
for
solder splashes and bridges.
2.
Check the interboard wiring to ensure that no
wires
are
"pinched"
or
contact
high-wattage
resistors.
3.
Check that all
control
knobs, shields, covers,
ground
straps,
and
mounting
hardware
have
been replaced. Be absolutely
certain
that you
have replaced
all
the
insulators.
4.
Look for unauthorized replacement parts, par-
ticularly transistors. that were installed during
a previous repair.
Point
them
out
to the
cus-
tomer
and
recommend their replacement.
5.
Look for parts which, though functioning, show
obvious signs of deterioration. Point them
out
to the customer and recommend their replace-
ment.
6.
Check the line cords for cracks and abrasion.
Recommend the replacement
of
any such line
cord
to
the customer.
7.
Check the B+ and
HV
to see
if
they are at the
values specified. Make sure
your
instruments
are
accurate;
be
suspicious of your
HV
meter
if
sets
always
have
low
HV.
8.
Check
the metal
trim,
metallized
knobs,
screws,
and all
other
exposed
metal
parts
for
AC
leakage.
Check leakage
as
described below.
To Exposed Metal
Parts on
Set
AC
voltmeter
(0.75V)
-=
Earth Ground
Fig.
A.
Using
an
AC voltmeter to check
AC
leakage.
LEAKAGE
TEST
The
AC
leakage from any exposed metal part to
earth ground and from all exposed metal parts to any
exposed metal part having a return to chassis, must
not
exceed
0.5mA
(500
microampers).
Leakage
current
can be
measured
by any one
of
three
methods.
l.
A
commercial
leakage
tester.
such as the
Simpson
229
or
RCA WT-540A.
Follow
the
manufactures' instructions
to
use these instru-
ments.
2.
A battery-operated
AC
milliammeter. The Data
Precision 245 digital multimeter is suitable for
this job.
3.
Measuring the voltage drop across a resistor by
means
of
a VOM or battery-operated
AC
volt-
meter.
The
"limit"
indication
is
0.75V.
so
analog
meters
must
have
an
accurate
low-
voltage
scale.
The
Simpson
250 and
Sanwa
SH-63Trd are examples
of
a passive VOM that
is suitable. Nearly all battery operated digital
multimeters
that
have
a 2V
AC
range are
suitable. (See Fig.
A)
HOW TO FIND A GOOD EARTH GROUND
A cold-water pipe is guaranteed earth ground; the
cover-plate retaining screw
on
most
AC
outlet boxes
is
also at earth ground.
If
the retaining screw is
to
be
used as your earth-ground, verify that it is at ground
by measuring the resistance between it and a cold-
water pipe with
an
ohmmeter. The reading should be
zero ohms.
If
a
cold-water
pipe
is not
accessible,
connect
a
60-100
watts
trouble
light
(not
a neon
lamp) between the hot side
of
the receptacle and the
retaining screw. Try both slots,
if
necessary,
to
locate
the
hot
side
of
the line. the
lamp
should
light
at
normal brilliance
if
the screw is at ground potential.
(Sec Fig.
B)
Trouble Light
Cold-water Pipe
Fig.
B.
Checking for earth ground.
-6-
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