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1 Safety Precautions
1.1. General Guidelines
1. Whenservicing, observe the original lead dress. If a short circuit is found, replace all parts which have been overheated or
damaged by the short circuit.
2. After servicing, ensure that all the protective devices such as insulation barriers, insulation papers shields are properly installe d.
3. After servicing, check for leakage current checks to prevent from beingexpose d to shock hazards.
1.1.1. Leakage Current Cold Check
1. Unplug the AC cord and connect a jumper between the two prongs on the plug.
2. Using anohmmeter measure the resistance value, between the jumpered AC plug and each exposed metalliccabine t part on
the equipment such as screwheads, connectors, control shafts, etc.When the exposedmetallic part has a return path to the
chassis, the reading should be between 1M-„¦and 5.2-„¦.
When theexpose d metal does not have a return path to the chassis, the reading must be
.
Figure 1
1.1.2. Leakage Current Hot Check (See Figure 1)
1. Plug the AC cord directly into the AC outlet. Do not use an isolatio n transformer for this check.
2. Conne ct a 1.5k-„¦, 10 watts resistor, in parallel with a 0.15µF capacitors, between each expose d metallic part on the set and a
good earth ground such as a water pipe, as shown in Figure 1.
3. Use an AC voltmeter, with 1000 ohms/volt or more sensitivity, to measure the potential across the resistor.
4. Check each expose d metallic part, and measure the voltage at each point.
5. Reverse the AC plug in the AC outlet and repeat each of the above measurements.
6. The potential at any point should not exceed 0.75 volts RMS. A leakage current tester (Simpson Model 229 or equivalent) may
be used to make the hot checks, leakage current must not exceed 1/2 milliamp. should the measurement is outside of the limits
specified, there is a possibility of a shock hazard, and the equipment should be repaired and re-checked before it is returned
to the customer.
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SB-WA101E / SB-WA101EB
