Sony KP 48S75 - Manual (Page 3)

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KP-43T75/48S75/
53N77/53S75/61S75
RM-Y906
SAFETY CHECK-OUT
( US model only )
After correcting the original service problem, perfom the follow-
ing safety checks before releasing the set to the customer:
l. 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 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 tran-
sistors, that were installed during a previous repair. Point them
out to the customer and recommend their replacement.
5. Look for parts which, through 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 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 temminals, 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 0.5mA (500 microampers) . Leak-
age 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
usc 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” indica-
tion is 0.75V, 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. NearIy all bat-
tery 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 re-
taining 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 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
AC
voltmeter
(0.75V)
1.5k Ω
Earth Ground
Fig. A. Using an AC voltmeter to check AC leakage.
1.5 µ F
Fig. B. Checking for earth ground.
Trouble Light
AC Outlet Box
Ohmmeter
Cold-water Pipe