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SAFETY CHECK-OUT
(US Model only)
After correcting the original service problem,
perform the following safety checks before releasing
the set to the customer:
1.
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
Tesistors.
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
=e
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.
1.
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.
(See Fig. B)
Trouble Light
() : AC Outlet Box
Ohmmeter
Cold-water Pipe
Fig. B. Checking for earth ground.
O e R S
| MOR TRE ae 2 E A e O
CO e e
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