Panasonic SDR-S50P Service Manual

31 Safety Precautions1.1. General Guidelines1. IMPORTANT SAFETY NOTICEThere are special components used in this equipment which are important for safety. These parts are marked by in theSchematic Diagrams, Circuit Board Layout, Exploded Views and Replacement Parts List. It is essential that these critical partsshould be replaced with manufacturer’s specified parts to prevent X-RADIATION, shock fire, or other hazards. Do not modifythe original design without permission of manufacturer.2. An Isolation Transformer should always be used during the servicing of AC Adaptor whose chassis is not isolated from the ACpower line. Use a transformer of adequate power rating as this protects the technician from accidents resulting in personalinjury from electrical shocks. It will also protect AC Adaptor from being damaged by accidental shorting that may occur duringservicing.3. 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.4. After servicing, see to it that all the protective devices such as insulation barriers, insulation papers shields are properlyinstalled.5. 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 the two prongs on the plug.2. Measure the resistance value, with an ohmmeter, between the jumpered AC plug and each exposed metallic cabinet part onthe equipment such as screwheads, connectors, control shafts, etc. When the exposed metallic part has a return path to thechassis, the reading should be between 1MΩ and 5.2MΩ. When the exposed metal does not have a return path to the chas-sis, the reading must be infinity.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” to exposed metallic part on the set. And con-nect “B” to a good earth ground, as shown in Figure 1.3. Use an AC voltmeter, with 1 kΩ/V or more sensitivity, tomeasure the potential across the resistor.4. Check each exposed metallic part, and measure the volt-age 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 0.25 V RMS.A leakage current tester (Simpson Model 229 or equiva-lent) may be used to make the hot checks, leakage cur-rent must not exceed 1/2 mA. In case a measurement isoutside of the limits specified, there is a possibility of ashock hazard, and the equipment should be repaired andrechecked before it is returned to the customer.Figure 1