Read Panasonic TX-21RX20T Service Manual online
1 Safety Precautions
1.1. General Guidelines
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 circuit is found,
2. When servicing, observe the original lead dress, especially the lead dress in the high voltage circuits. If a short circuit 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 power socket.
5. Potential, as high as 25.0 kV is present when this receiver is in operation. Operation of the receiver without the rear cover
5. Potential, as high as 25.0 kV 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 check to
prevent the customer from being exposed to shock hazards.
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 check to
prevent the customer from being exposed to shock hazards.
1.2. Leakage Current Cold Check
1. Unplug the power cord and connect a jumper between the two prongs on the plug.
2. Turn on the receiver’s power switch.
2. Turn on the receiver’s power switch.
Measure the resistance value, with an ohmmeter, between the jumper 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 4 M
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 4 M
Ω and 20 MΩ. When the exposed metal does not have a return path to the chassis, the
reading must be infinite.
1.3. Leakage Current Hot Check (Fig. 1)
1. Plug the power cord directly into the power socket. Do not use an isolation transformer for this check.
2. Check that a 2 k
2. Check that a 2 k
Ω non-inductive resistor and an AC/DC current meter are 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 2 mA DC. In the case of a measurement 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.
The current from any point should not exceed 0.7 mA peak AC or 2 mA DC. In the case of a measurement 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
3
TX-21RX20T
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