KV-21XE42C - Sony TV Service Manual (repair manual). Page 7

After correcting the original service problem, perform the
following safety checks before releasing the set to the
customer:

        

   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 microampere).
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 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's 250 and Sanwa
SH-63Trd are examples of passive VOMs that are suitable.
Nearly all battery operated digital multimeters that have a
2V AC range are suitable.   (See Fig. A)

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 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 specified

values.  Make sure your instruments are accurate;
be suspicious of your HV meter if sets always have
low HV.

8. Check the antenna terminals, metal trim, “metallized"

knobs, screws, and all other exposed metal parts for
AC Leakage.  Check leakage as described below.

   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-l00 watts
trouble light (not a neon lamp) between the hot side of the re-
ceptacle 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)

1.5 k

W

0.15 µF

AC
Voltmeter
(0.75 V)

To Exposed Metal
Parts on Set

Earth Ground

Fig. A. Using an AC voltmeter to check AC leakage.