Sony SLV-478 Service Manual page 3

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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. Look for unauthorized replacement parts, particularly
transistors, that were installed during a previous repair. Point
them out to the customer and recommend their replacement.
4. Look for parts which, though functioning, show obvious signs
of deterioration. Point them out to the customer and
recommend their replacement.
5. Check the line cord for cracks and abrasion.
Recommend the replacement of any such line cord to the
customer.
6. Check the B+ voltage to see it is at the values specified.
7. 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
TE
L 13942296513
0.15 µ F
Fig. A. Using an AC voltmeter to check AC leakage.
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SAFETY CHECK-OUT
After correcting the original service problem, perform the following
safety checks before releasing the set to the customer.
Parts on Set
AC
Voltmeter
1.5 k Ω
(0.75 V)
Earth Ground
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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).
Leakage current can be measured by any one of three methods.
1. A commercial leakage tester, such as the Simpson 229 or RCA
TW-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" indication
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. Nearly all battery operated
digital multimeters that have a 2V AC range are suitable. (See
Fig. A)
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