Safety Precautions; General Guidelines; Leakage Current Cold Check; Leakage Current Hot Check - Panasonic PT-50LCZ70 Service Manual

1 Safety Precautions

1.1.

General Guidelines

1. For continued safety, no modification of any circuit should
be attempted.
2. Disconnect AC Plug before disassembling this unit.
3. It is advisable to use an isolation transformer in the AC
supply before servicing.
4. When servicing, observe the original lead dress. If a short
circuit is found, replace all parts which have been
overheated or damaged by the short circuit.
5. After servicing, see to it that all the protective devices such
as insulation barriers, insulation papers, shield, and
isolation R-C combinations etc. are properly installed.
6. After servicing, be sure to restore the wires, leads,
insulation barriers, shields, etc.
7. After servicing, make the leakage current checks to prevent
the customer from being exposed to shock hazards.
Caution:
Use a separate Isolation Transformer for this unit when
servicing.
1.2.

Leakage Current Cold Check

1. Unplug the AC cord and connect a jumper between the two
prongs on the plug.
2. For physically operated power switches, turn power on.
Otherwise skip step 2.
3. Measure the resistance value, with an ohmmeter, between
the jumpered AC plug and each exposed metallic cabinet
part on the receiver, such as screwheads, connectors, etc.
When the exposed metallic part has a return path to the
chassis, the reading should be between 1 MΩ and 12 MΩ.
When the exposed metal does not have a return path to the
chassis, the reading must be infinity.
1.3.

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" to exposed metallic part on the set. And
connect "B" to a good earth ground, as shown in Figure 1.
3. Use an AC voltmeter, with 1 kΩ/V or more sensitivity, to
measure 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 0.25 V RMS.
A leakage current tester (Simpson Model 228 equivalent)
may be used to make the hot checks. Leakage current must
not exceed 1/2 mA. In case a measurement is outside of
the limits specified, there is a possibility of shock hazard,
and the receiver should be repaired and rechecked before
it is returned to the customer.
PT-50LCZ70 / PT-56LCZ70 / PT-61LCZ70 / PT-50LCZ7 / PT-56LCZ7 / PT-61LCZ7
1.4.

Disposal Lamp

3
Figure 1