Panasonic TX-25MK1 Service Manual

Also see for TX-25MK1: Operating instructions

Contents

CONTENTSSAFETY PRECAUTIONS..........................................................................................................................................................2SERVICE HINTS .......................................................................................................................................................................3SERVICE POSITION.................................................................................................................................................................4ADJUSTMENT PROCEDURE AND FACTORY SETTINGS .....................................................................................................5WAVEFORM PATTERN TABLE ...............................................................................................................................................6ALIGNMENT SETTINGS...........................................................................................................................................................7BLOCK DIAGRAMS ..................................................................................................................................................................8PARTS LOCATION .................................................................................................................................................................12REPLACEMENT PARTS LIST ................................................................................................................................................13SCHEMATIC DIAGRAMS .......................................................................................................................................................22CONDUCTOR VIEWS.............................................................................................................................................................26SAFETY PRECAUTIONSGENERAL GUIDE LINES1. It is advisable to insert an isolation transformer in thea.c. supply before servicing a hot chassis.2. When servicing, observe the original lead dress in thehigh voltage circuits. If a short circuit is found, replaceall parts that have been overheated or damaged bythe short circuit.3. After servicing, see that all the protective devicessuch as insulation barriers, insulation papers, shieldsand isolation R-C combinations are correctlyinstalled.4. When the receiver is not being used for a long periodof time, unplug the power cord from the a.c. outlet.5. Potentials as high as 29,2kV are present when thisreceiver is in operation. Operation of the receiverwithout the rear cover involves the danger of a shockhazard from the receiver power supply. Servicingshould not be attempted by anyone who is notfamiliar with the precautions necessary when workingon high voltage equipment. Always discharge theanode of the tube.6. After servicing make the following leakage currentchecks to prevent the customer from being exposedto shock hazard.LEAKAGE CURRENT COLD CHECK1. Unplug the a.c. cord and connect a jumper betweenthe two prongs of the plug.2. Turn on the receiver’s power switch.3. Measure the resistance value with an ohmmeter,between the jumpered a.c. plug and each exposedmetallic cabinet part on the receiver, such as screwheads, aerials, connectors, control shafts etc. Whenthe exposed metallic part has a return path to thechassis, the reading should be between 4M ohm and20M ohm. When the exposed metal does not have areturn path to the chassis, the reading must beinfinite.LEAKAGE CURRENT HOT CHECK1. Plug the a.c. cord directly into the a.c. outlet. Do notuse an isolation transformer for this check.2. Connect a 2kΩ 10W resistor in series with anexposed metallic part on the receiver and an earth,such as a water pipe.3. Use an a.c. voltmeter with high impedance tomeasure the potential across the resistor.4. Check each exposed metallic part and check thevoltage at each point.5. Reverse the a.c. plug at the outlet and repeat each ofthe above measurements.6. The potential at any point should not exceed1,4Vrms. In case a measurement is outside the limitsspecified, there is a possibility of a shock hazard, andthe receiver should be repaired and rechecked beforeit is returned to the customer.X-RADIATION WARNING1. The potential sources of X-Radiation in TV sets arethe high voltage section and the picture tube.2. When using a picture tube test jig for service, ensurethat the jig is capable of handling 29,2kV withoutcausing X-Radiation.NOTE: It is important to use an accurate periodicallycalibrated high voltage meter.1. Set the brightness to minimum.2. Measure the high voltage. The meter should indicate.28,2kV ± 1kV. If the meter indication is out oftolerance, immediate service and correction isrequired to prevent the possibility of prematurecomponent failure.3. To prevent any X-Radiation possibility, it is essentialto use the specified tube.HOT CHECK CIRCUITa.c. VOLTMETERWATER PIPE(EARTH)TO INSTRUMENT’S EXPOSEDMETALLIC PARTS Fig. 1.2kΩ 10 Watts2