Panasonic HM-TA2PC Service Manual

Contents

31 Safety Precautions1.1. General Guidelines1. IMPORTANT SAFETY NOTICEThere are special components used in this equipmentwhich are important for safety. These parts are marked byin the Schematic Diagrams, Circuit Board Layout,Exploded Views and Replacement Parts List. It is essen-tial that these critical parts should be replaced with manu-facturer’s specified parts to prevent X-RADIATION,shock, fire, or other hazards. Do not modify the originaldesign without permission of manufacturer.2. An Isolation Transformer should always be used duringthe servicing of AC Adaptor whose chassis is not isolatedfrom the AC power line. Use a transformer of adequatepower rating as this protects the technician from acci-dents resulting in personal injury from electrical shocks. Itwill also protect AC Adaptor from being damaged by acci-dental shorting that may occur during servicing.3. When servicing, observe the original lead dress. If a shortcircuit is found, replace all parts which have been over-heated or damaged by the short circuit.4. After servicing, see to it that all the protective devicessuch as insulation barriers, insulation papers shields areproperly installed.5. After servicing, make the following leakage currentchecks to prevent the customer from being exposed toshock hazards.1.2. 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 exposed metal-lic cabinet part on the equipment such as screwheads,connectors, control shafts, etc. When the exposed metal-lic part has a return path to the chassis, the readingshould be between 1 MΩ and 5.2 MΩ. When the exposedmetal does not have a return path to the chassis, thereading must be infinity.1.3. 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 1.5 kΩ, 10 W resistor, in parallel with a 0.15 μFcapacitor, between each exposed metallic part on the setand 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 0.75 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