PANASONIC TXW28R4L
Manual de Servicio

CONTENTS
SAFETY PRECAUTIONS..........................................................................................................................................................2 SERVICE HINTS .......................................................................................................................................................................3 SERVICE POSITION.................................................................................................................................................................4 ADJUSTMENT PROCEDURE...................................................................................................................................................5 ADJUSTMENT PROCEDURE AND SELF-CHECK ..................................................................................................................6 WAVEFORM PATTERN TABLE ...............................................................................................................................................7 ALIGNMENT SETTINGS...........................................................................................................................................................8 BLOCK DIAGRAMS ..................................................................................................................................................................9 PARTS LOCATION .................................................................................................................................................................13 REPLACEMENT PARTS LIST ................................................................................................................................................14 SCHEMATIC DIAGRAMS .......................................................................................................................................................24 CONDUCTOR VIEWS.............................................................................................................................................................27

SAFETY PRECAUTIONS
GENERAL GUIDE LINES
1. 2. It is advisable to insert an isolation transformer in the AC supply before servicing a hot chassis. When servicing, observe the original lead dress in the high voltage circuits. If a short circuit is found, replace all parts that have been overheated or damaged by the short circuit. After servicing, see that all the protective devices such as insulation barriers, insulation papers, shields and isolation R-C combinations are correctly installed. When the receiver is not being used for a long period of time, unplug the power cord from the AC outlet. Potentials as high as 31,5kV are present when this receiver is in operation. Operation of the receiver without the rear cover involves the danger of a shock hazard from the receiver power supply. Servicing should not be attempted by anyone who is not familiar with the precautions necessary when working on high voltage equipment. Always discharge the anode of the tube. After servicing make the following leakage current checks to prevent the customer from being exposed to shock hazard. Unplug the AC cord and connect a jumper between the two prongs of the plug. Turn on the receiver�s power switch. Measure the resistance value with an ohmmeter, between the jumpered AC plug and each exposed metallic cabinet part on the receiver, such as screw heads, aerials, connectors, control shafts etc. When the exposed metallic part has a return path to the chassis, the reading should be between 4M ohm and 20M ohm. When the exposed metal does not have a return path to the chassis, the reading must be infinite. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check. Connect a 2k� 10W resistor in series with an exposed metallic part on the receiver and an earth, such as a water pipe. Use an AC voltmeter with high impedance to measure the potential across the resistor. Check each exposed metallic part and check the voltage at each point. 5. Reverse the AC plug at the outlet and repeat each of the above measurements. The potential at any point should not exceed 1,4 Vrms. In case a measurement is outside the limits specified, there is a possibility of a shock hazard, and the receiver should be repaired and rechecked before it is returned to the customer.

6.

3.

HOT CHECK CIRCUIT
A.C. VOLTMETER

4. 5.

2k� 10 Watts TO INSTRUMENT�S EXPOSED METALLIC PARTS

6.

WATER PIPE (EARTH)

LEAKAGE CURRENT COLD CHECK
1. 2. 3.

Fig. 1.

X-RADIATION WARNING
1. 2. The potential sources of X-Radiation in TV sets are the high voltage section and the picture tube. When using a picture tube test jig for service, ensure that the jig is capable of handling 30,5kV without causing X-Radiation.

LEAKAGE CURRENT HOT CHECK
1. 2.

3. 4.

NOTE: It is important to use an accurate periodically calibrated high voltage meter. 1. Set the brightness to minimum. 2. Measure the high voltage. The meter should indicate :- 31,5kV ± 1kV. If the meter indication is out of tolerance, immediate service and correction is required to prevent the possibility of premature component failure. 3. To prevent any X-Radiation possibility, it is essential to use the specified tube.

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