Safety Precautions; General Guidelines; Touch-Current Check - Panasonic TX-P42G20E Service Manual

1 Safety Precautions

1.1.

General Guidelines

1. 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.
2. After servicing, see to it that all the protective devices such as insulation barriers, insulation papers shields are properly
installed.
3. After servicing, make the following leakage current checks to prevent the customer from being exposed to shock hazards.
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 shields are properly
installed.
6. After servicing, make the following leakage current checks to prevent the customer from being exposed to shock hazards.
1.2.

Touch-Current Check

1. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check.
2. Connect a measuring network for touch currents between each exposed metallic part on the set and a good earth ground
such as a water pipe, as shown in Figure 1.
3. Use Leakage Current Tester (Simpson 228 or equivalent) to measure the potential across the measuring network.
4. Check each exposed metallic part, and measure the voltage at each point.
5. Reserve the AC plug in the AC outlet and repeat each of the above measure.
6. The potential at any point (TOUGH CURRENT) expressed as voltage U
For a. c.: U = 35 V (peak) and U
1
For d. c.: U = 1.0 V,
1
Note:
The limit value of U
mA d. c.
The limit value U
7. In case a measurement is out of the limits specified, there is a possibility of a shock hazard, and the equipment should be
repaired and rechecked before it is returned to the customer.
= 0.35 V (peak);
2
= 0.35 V (peak) for a. c. and U
2
= 35 V (peak) for a. c. correspond to the value 70 mA (peak) a. c. for frequencies greater than 100 kHz.
1
and U , does not exceed the following values:
1 2
= 1.0 V for d. c. correspond to the values 0.7 mA (peak) a. c. and 2.0
1
Figure 1
3