1 (P)
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 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, particularly transistors,
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 recommend
their replacement.
6. Check the line cord for cracks and abrasion. Recommend the
replacement of any such line cord to the customer.
7. Check the condition of the monopole antenna (if any).
Make sure the end is not broken off, and has the plastic cap on
it. Point out the danger of impalement on a broken antenna to the
customer, and recommend the antenna’s replacement.
8. Check the B+ and HV to see they are at the values specified.
Make sure your instruments are accurate; be suspicious of your
HV meter if sets always have low HV.
9. Check the antenna terminals, metal trim, “metallized” knobs,
screws, and all other exposed metal parts for AC leakage.
Check leakage as described below.
LEAKAGE
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 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 manufacturers’ instructions to use these
instruments.
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 voltmeter. The “limit” indication
is 0.75 V, 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 coldwater
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)
To Exposed Metal
Parts on Set
1.5kΩ
0.15µF
Earth Ground
AC
voltmeter
(0.75V)
Fig. A. Using an AC voltmeter to check AC leakage.
Cold-water Pipe
Ohmmeter
AC Outlet Box
Trouble Light
Fig. B. Checking for earth ground.
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