Panasonic TC-29P10N, Service Manual, Page: 3 / 61

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Safety Precautions
General Guide Lines
1. It is advisable to insert an isolation transformer in the AC
supply before servicing a hot chassis.
2. When servicing, observe the original lead dress, espe-
cially 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 be used for a long period of
time, unplug the power cord from the AC outlet.
5. Potential, as high as
33.0 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 volt-
age equipment. Always discharge the anode of the pic-
ture tube to the receiver chassis before handling the
tube.
6. 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.
3. 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 4 MW and 20 MW.
When the exposed metal does not have a return path to
the chassis, the reading must be •.
Leakage Current Hot Check
1. Plug the AC cord directly into the AC outlet. Do not use
an isolation transformer for this check.
2. Connect a 2kW, 10W resistor, in series with an exposed
metallic part on the receiver and an earth such as a
water pipe.
3. Use an AC voltmeter, with high impedance type, to mea-
sure the potential across the resistor.
4. Check each exposed metallic part, and measure the
voltage at each point.
5. Reverse the AC plug in the AC outlet and repeat each of
the above measurements.
6. The potential at any point should not exceed
1.0 Vrms
.
In case a measurement is outside of 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.
Isolation Transformer
power-on
Hot-Check Circuit
AC Voltmeter
To
Instrument's
Metallic Parts
Exposed
Water Pipe
(Earth)
2 k
W
10W
!"