Panasonic TX-21PM30T, Service Manual

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Safety Precautions
General Guide Lines
1. It is advisable to insert an isolation transformer in the AC supply before servicing this hot chassis.
2. When servicing, observe the original lead dress, especially the lead dress in the high voltage circuits. If
a short circuits is found, replace all parts which have been overheated or damaged by the short circuit.
3. After servicing, see to it that all the protective devices such as insulation barriers, insulation papers,
shields, and isolation R-C combinations, are properly installed.
4. When the receiver is not to be used for a long period of time, unplug the power cord from the AC cord
outlet.
5. Potential, as high as 28.0kV. is 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 thoroughly familiar with the precautions necessary when
working on high voltage equipment. Always discharge the anode of the picture tube to the receiver
chassis before handling the tube.
After servicing make the following leakage current checks to prevent the customer from being exposed
to shock hazards.
Leakage Current Cold Check
1. Unplug the AC cord and connect a jumper between the two prongs on the plug.
2. Turn on the receiver’s power switch.
Measure the resistance value, with an ohmmeter, between the jumper AC plug and each exposed metal-
lic cabinet part on the receiver, such as screw heads, aerials, connectors, control shafts, ect. When the
exposed metallic part has a return path to the chassis, the reading should be between 4 Mohm and 20
Mohm.When the exposed metal does not have a return path to the chassis, the reading must be infinite.
Leakage Current Hot Check ( Fig.1 )
1. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check.
2. Check a 2 kohm non-inductive resistor and an AC/DC current meter, in series with each exposed
metallic part on the receiver in turn and an earth such as a water pipe.
The current from any point should not exceed 0.7 mA peak AC or 2mA DC. In the case of a measure-
ment being outside of these 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.
Fig.1