Panasonic DMR-BWT720EB Service Manual

Contents

51 Safety Precautions1.1. General guidelines1. When servicing, observe the original lead dress. If a short circuit is found, replace all parts which have been overheated ordamaged by the short circuit.2. After servicing, see to it that all the protective devices such as insulation barriers, insulation papers shields are properlyinstalled.3. After servicing, make the following leakage current checks to prevent the customer from being exposed to shock hazards.1.1.1. Leakage current cold check1. Unplug the AC cord and connect a jumper between thetwo prongs on the plug.2. Measure the resistance value, with an ohmmeter,between the jumpered AC plug and each exposedmetallic cabinet part on the equipment such asscrewheads, connectors, control shafts, etc. When theexposed metallic part has a return path to the chassis, thereading should be between 1MΩ and 5.2MΩ.When the exposed metal does not have a return path tothe chassis, the reading must be .1.1.2. Leakage current hot check(See Figure 1.)1. Plug the AC cord directly into the AC outlet. Do not usean isolation transformer for this check.2. Connect a 1.5kΩ, 10 watts resistor, in parallel with a0.15μF capacitors, between each exposed metallic parton 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 moresensitivity, to measure the potential across the resistor.4. Check each exposed metallic part, and measure thevoltage at each point.5. Reverse the AC plug in the AC outlet and repeat each ofthe above measurements.6. The potential at any point should not exceed 0.75 voltsRMS. A leakage current tester (Simpson Model 229 orequivalent) may be used to make the hot checks, leakagecurrent must not exceed 1/2 milliampere. In case ameasurement is outside of the limits specified, there is apossibility of a shock hazard, and the equipment shouldbe repaired and rechecked before it is returned to thecustomer.Figure 1