Sony KL-W9000 - Manual (Page 3)

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KL-W7000/W9000
RM-Y980
SAFETY CHECK-OUT
(US Model only)
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 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” indica-
tion is 0.75 V, so analog meters must have an accurate low-
voltage scale. The Simpson 250 and Sanwa SH-63Trd are ex-
amples of a passive VOMs that are suitable. Nearly all battery
operated digital multimeters that have a 2 V AC range are suit-
able. (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 cold-
water 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 recep-
tacle 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)
After correcting the original service problem, perform the fol-
lowing safety checks before releasing the set to the customer:
1. 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 transis-
tors, 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 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 if they are specified values. 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.
1.5 k
Ω
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.
Trouble Light
AC Outlet Box Ohmmeter
Cold-water Pipe
Fig. B. Checking for earth ground.