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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 sol-
dered connections. Check the entire board surface for solder
splashes and bridges.
2. Check the interboard wiring to ensure that no wires are
"pinched" or touching high-wattage resistors.
3. Check that all control knobs, shields, covers, ground straps,
and mounting hardware have been replaced. Be absolutely cer-
tain that you have replaced all the insulators.
4. Look for unauthorized replacement parts, particularly transis-
tors, that were installed during a previous repair. Point them
out to the customer and recommend their replacement.
5. Look for parts which, though functioning, show obvious signs
of deterioration. Point them out to the customer and recom-
mend their replacement.
6. Check the line cords for cracks and abrasion. Recommend the
replacement of any such line cord to the customer.
7. Check the antenna terminals, metal trim, "metallized" knobs,
screws, and all other exposed metal parts for AC leakage. Check
leakage as described below.
0.15 μ F
Figure A. Usingan AC voltmeter to check AC leakage.
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To Exposed Metal
Parts on Set
Earth Ground
SAFETY CHECK-OUT
LeakageTest
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 0.5 mA (500 microamperes).
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 manufacturers' instructions to use these
instructions.
2. A battery-operated AC milliampmeter. 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 voltmeter. The "limit" indica-
tion is 0.75V, so analog meters must have an accurate low volt-
age scale.
The Simpson's 250 and Sanwa SH-63TRD are examples of
passive VOMs that are suitable. Nearly all battery-operated
digital multimeters that have a 2 VAC range are suitable (see
Figure A).
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How to Find a Good Earth Ground
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A cold-water pipe is a guaranteed earth ground; the cover-plate
retaining screw on most AC outlet boxes is also at earth ground. If
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the retaining screw is to be used as your earth ground, verify that
or AC
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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
If a cold-water pipe is not accessible, connect a 60- to 100-watt
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trouble- light (not a neon lamp) between the hot side of the
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brilliance if the screw is at ground potential (see Figure B).
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AC
Voltmeter
(0.75V)
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Figure B. Checking for earth ground.
KLV-32/37M300A
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