Panasonic TX-23LX50M Service Manual

Also see for TX-23LX50A: Operating instructions

Panasonic TX-23LX50M Service Manual Manual pdf 4 page image

1.1.1. Leakage Current Cold Check1. Unplug the AC cord and connect a jumper between the twoprongs on the plug.2. Measure the resistance value, with an ohmmeter, betweenthe jumpered AC plug and each exposed metallic cabinetpart on the equipment such as screwheads, connectors,control shafts, etc. When the exposed metallic part has areturn path to the chassis, the reading should be between1M and 5.2M.When the exposed metal does not have a return path to thechassis, the reading must be .Figure 11.1.2. Leakage Current Hot Check (SeeFigure 1.)1. Plug the AC cord directly into the AC outlet. Do not use anisolation transformer for this check.2. Connect a 1.5k, 10 watts resistor, in parallel with a 0.15μFcapacitors, between each exposed metallic part on the setand a good earth ground such as a water pipe, as shown inFigure 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 of theabove 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 milliamp. In case ameasurement is outside of the limits specified, there is apossibility of a shock hazard, and the equipment should berepaired and rechecked before it is returned to thecustomer.1 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.2 Prevention of Electro Static Discharge (ESD) toElectrostatically Sensitive (ES) DevicesSome semiconductor (solid state) devices can be damaged easily by static electricity. Such components commonly are calledElectrostatically Sensitive (ES) Devices. Examples of typical ES devices are integrated circuits and some field-effect transistors andsemiconductor "chip" components. The following techniques should be used to help reduce the incidence of component damagecaused by electro static discharge (ESD).1. Immediately before handling any semiconductor component or semiconductor-equipped assembly, drain off any ESD on yourbody by touching a known earth ground. Alternatively, obtain and wear a commercially available discharging ESD wrist strap,which should be removed for potential shock reasons prior to applying power to the unit under test.2. After removing an electrical assembly equipped with ES devices, place the assembly on a conductive surface such as alminumfoil, to prevent electrostatic charge buildup or exposure of the assembly.3. Use only a grounded-tip soldering iron to solder or unsolder ES devices.4. Use only an anti-static solder removal device. Some solder removal devices not classified as "anti-static (ESD protected)" cangenerate electrical charge sufficient to damage ES devices.5. Do not use freon-propelled chemicals. These can generate electrical charges sufficient to damage ES devices.6. Do not remove a replacement ES device from its protective package until immediately before you are ready to install it. (Mostreplacement ES devices are packaged with leads electrically shorted together by conductive foam, alminum foil or comparableconductive material).7. Immediately before removing the protective material from the leads of a replacement ES device, touch the protective materialto the chassis or circuit assembly into which the device will be installed.4TX-23LX50M / TX-23LX50A / TX-23LX50X