TX-L42FT60B, TX-LR42FT60 - Panasonic TV Service Manual (repair manual). Page 3

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Safety Precautions
General Guide Lines
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 touch current checks to prevent the customer from being exposed to shock hazards. 
4.  Always ensure cover label TBM4GU113 is correctly replaced before returning to customer (see Fig.1). 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
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 Fig. 2. 
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 (TOUCH CURRENT) expressed as voltage U1 and U2, does not exceed the following values: 
For a. c.: U1 = 35 V (peak) and U2 = 0.35 V (peak); 
For d. c.: U1 = 1.0 V, 
Note:
 
The limit value of U2 = 0.35 V (peak) for a. c. and U1 = 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 U1 = 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 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. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 2 
TO 
APPLIANCES 
EXPOSED 
METAL PARTS 
Resistance values in ohms (
) 
R
0
=500
 
R
S
=1500
 
C
S
=0.22
F 
10k
 
0.022
F 
COLD 
WATER PIPE 
(EARTH GROUND)
 
V: Voltmeter or oscilloscope 
  (r.m.s. or peak reading) 
Measuring network for TOUCH CURRENTS 
Input resistance: 
1M 
Input capacitance:
200pF 
Frequency range: 15Hz to 1MHz and d.c.respectively 
NOTE – Appropriate measures should be taken to obtain the correct value in case of non-sinusoidal waveforms 
U
2
 (V) 
Fig. 1 
U
1
 (V) 
3
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