1
KLV-20/32/37/40S400A (CH) 5
SAFETY CHECK-OUT
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 touching 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 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.
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 0.5 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”
indication is 0.75 V, so analog meters must have an accurate
low voltage 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).
How to Find a Good Earth Ground
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 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- to 100-watt
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 on the line; the lamp should light at normal
brilliance if the screw is at ground potential (see Figure B).
To Next Page
Loading...
