Sony KV-20V50 Service Manual page 3

Aftercorrectingtheoriginal
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 unauthorizedreplacement 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
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.
To Exposed Metal
Parts on Set
= Earth Ground
Fig. A. Using an AC voltmeter to check AC leakage.
SAFETY CHECK-OUT
(US Model only)
LEAKAGE
from all exposed metal parts to any exposed metal part having a return
to chassis, must not exceed 0.5 mA (500 microampers).
current can be measured by any one of three methods.
1.
2.
3.
HOW TO FIND A GOOD EARTH GROUND
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
antenna (if any).
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)
AC
voltmeter
The AC leakage from any exposed metal part to earth ground and
A commercial leakage tester, such as the Simpson 229 or RCA
Follow the manufacturers' instructions to use these
instruments.
A battery-operated AC milliammeter. The Data Precision 245
digital multimeter is suitable for this job.
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)
A cold-water pipe is guaranteed earth
Trouble Light
Fig. B. Checking for earth ground.
Leakage
ground; the cover-plate
Cold-water Pipe