Panasonic TX-29FG20R Service Manual

Panasonic TX-29FG20R Service Manual Manual pdf 3 page image

1 Safety Precautions1.1. General Guide1. It is advisable to insert an isolation transformer in the ACsupply before servicing a hot chassis. Fig. 1.Fig. 12. When servicing, observe the original lead dress, especiallythe lead dress in the high voltage circuits. If a short circuit isfound, replace all parts which have been overheated ordamaged by the short circuit.3. After servicing, observe that all the protective devices suchas insulation barriers, insulation papers, shields, andisolation R-C combinations, are properly installed.4. When the receiver is not to be used for a long period oftime, unplug the power cord from the AC outlet.5. Potential, as high as 32kV kV is present when this receiveris in operation. Operation of the receiver without thereceiver power supply. Servicing should not be attemptedby anyone who is not thoroughly familiar with theprecautions necessary when working on high voltageequipment. Always discharge the anode of the picture tubeto the receiver chassis before handling the tube.After servicing make the following leakage current checks toprevent the customer from being exposed to shockhazards.1.2. Leakage Current Cold Check1. Unplug the AC cord and connect a jumper between the twoprongs on the plug. Fig. 2.Fig. 22. Turn on the receiver’s power switch.3. Measure the resistance value, with an ohmmeter, betweenthe jumpered AC plug and each exposed metallic cabinetpart on the receiver, such as screw heads, aerials,connectors, control shafts, etc. When the exposed metallicpart has a return path to the chassis, the reading should bebetween 4 MΩΩΩΩ and 20 MΩΩΩΩ. When the exposed metal doesnot have a return path to the chassis, the reading must bezero.1.3. Leakage Current Hot Check(See Fig. 1)1. Plug the AC cord directly into the AC outlet. Do not use anisolation transformer for this check.2. Connect a 2 kΩ, 10 W resistor in series with an exposedmetallic part on the receiver and an earth such as a waterpipe.3. Use an AC voltmeter, with high impedance type, tomeasure the potential across the resistor.4. Check each exposed metallic part, and measure thevoltage at each point. Fig. 3.Fig. 35. Reverse the AC plug in the AC outlet and repeat each of theabove measurements.6. The potential any point should not exceed 1.0 V rms. In thecase of a measurement being outside of the limits specified,there is a possibility of a shock hazard, and the receivershould be repaired and re-checked before it is returned tothe customer. Fig. 4.Fig. 41.4. X-RadiationWarning :1. The potential sources of X-Radiation in TV sets are the EHTsection and the picture tube.2. When using a picture tube test rig for service, ensure thatthe rig is capable of handling 30 kV without causing X-Radiation.Note: It is important to use an accurate periodically calibratedhigh voltage meter.1. Set the brightness to minimum.2. Measure the High Voltage. The meter reading shouldindicate 31.0 ± 1.0kV. If the meter indication is out oftolerance, immediate service and correction is required toprevent the possibility of premature component failure.3. To prevent the possibility of X-Radiation, it is essential touse the specified picture tube.3TX-29FG20R