Panasonic TC-21FX30LA, Service Manual

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TC-21FX30LA/LP / TC-29FX30LA/LP
SAFETY PRECAUTIONS
General Guide Lines
1. It is advisable to insert an insulation 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, 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 insulation
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 29.0kV 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 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
Ω
. and 20M
Ω
. 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 insulation transformer for this check.
2. Use a non inductive 2K
Ω
10W resistor in series with an exposed metallic part of the receiver and earth such as a water pipe.
3. Using a high impendance AC voltimeter, check the resistor’s potential.
4. Check each metallic part of the receiver.
5. Invert the plug of the AC chord and repeat all measurements.
6. The voltage from any point should not exceed 1.0V
RMS
. In case of a measurement is 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.
X-Radiation
Warning:
The potential sources of X-Radiation in TV set are the EHT section and the picture tube. When using a picture tube test jig
for service, ensure that jig is capable of handling 29.0kV without causing X-Radiation.
Note: It is important to use an accurate periodically calibrated high voltage meter.
1. Set the brightness to minimum.
2. Use the remocon to get into Service Mode.
3. Measure the EHT. The meter reading should indicate 27.5±1.5kV. If the meter indication is out of tolerance, immediate
service and correction is required to prevent the possibility of premature component failure.
4. To prevent the possibility X-Radiation, it is essential to use the specified picture tube, if service replacement becomes
necessary.
Hot - Check Circuit
Water Pipe
(Earth)
To
instrument’s
Metallic Parts
Exposet
AC Voltimeter
Fig. 1