Panasonic TX-PR42G10, Service Manual

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1 Safety Precautions
1.1. General Guidelines
1. W hen 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. A fter servicing, make the following leakage current checks to prevent the custom er from being exposed to shock hazards.
4. W hen 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. A fter servicing, see to it that all the protective devices such as insulation barriers, insulation papers shields are properly
installed.
A fter servicing, make the following leakage current checks to prevent the custom er from being exposed to shock hazards. 6
1.2. Touch-Current Check
1. Plug the AC cord directly into the AC outlet. Do not use an isolation transform er 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 w ater 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
1
and U
2
, does not exceed the following values:
For a. c.: U
1
= 35 V (peak) and U
2
= 0.35 V (peak);
For d. c.: U1 = 1.0 V,
Note:
The limit value of U
2
= 0.35 V (peak) for a. c. and U
1
= 1.0 V for d. c. correspond to the values 0.7 mA (peak) a. c. and 2.0
mA d. c.
The limit value U
1
= 35 V (peak) for a. c. correspond to the value 70 mA (peak) a. c. for frequencies greater than 100 kHz.
7. In case a m easurement is out of the limits specified, there is a possibility of a shock hazard, and the equipm ent should be
repaired and rechecked before it is returned to the customer.
Measuring network for TOUCH CURRENTS
COLD
WATER PIPE
(EARTH GROUND)
Rs=
1500Q
_ L Cs=
0.22|
j
F
10kQ
-1
k 1 -------
1
Ro=
----------------
J
500Q
'
U
1
=
r
= 0.022|jF
(V)
JQ LjJ JUUii U
1
—|— и.и^гф Г ^ V
J
| U
2
(V)
APPLIANCES
EXPOSED
METAL PARTS
Resistance values in ohms (Q)
V: Voltmeter or oscilloscope
(r.m.s. or peak reading)
Input resistance: > 1 MQ
Input capacitance: < 200 pF
Frequency range: 15 Hz to 1 MHz and d.c. respectively
NOTE - Appropriate measures should be taken to obtain the correct value in case of non-sinusoidal waveforms.
Figure 1
2