SONY KP43T70
Service Manual

KP-43T70/46C70/48S70/ 48S72/53N74/53S70/61S70 SAFETY CHECK-OUT
( US model only )

RM-Y906

After correcting the original service problem, perfom the following safety checks before releasing the set to the customer: l. 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, 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) . 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 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� indication is 0.75V, so analog meters must have an accurate lowvoltage scale. The Simpson 250 and Sanwa SH-63Trd are examples of a passive VOM that is suitable. NearIy all battery 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 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 coldwater 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

Trouble Light Ohmmeter AC Outlet Box
AC voltmeter (0.75V)

1.5 µ F

1.5k �

Cold-water Pipe

Earth Ground

Fig. B. Checking for earth ground.
Fig. A. Using an AC voltmeter to check AC leakage.

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