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1. Safety Instruction
1.1. General Guidelines
1. When servicing, observe the original lead dress. If a short circuit is found, replace all part
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.
1.2. Touch-Current Check
1. Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this chack.
2. Connect a measuring network for touch currents between each exposed matallic part on
the set and a good earth ground such as a water pipe, as shown in Figure1.
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.
6. The potential at any point (TOUGH CURRENT) expressed as voltage U
exceed the following values:
For a. c.: U
= 35V(peak) and U
1
For d. c.: U
= 1.0V,
1
Note:
The limit value of U
values 0.7 mA (peak) a. c. and 2.0 mA d. c.
The limit value U
frequencies greater than 100kHz.
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.
COLD
WATER PIPE
(EARTH
GROUND
TO
APPLIANCES
EXPOSED
METAL PARTS
Resistance values in ohms(
V: Voltmeter or oscilloscope(r.m.s. or peak reading)
Input resistance:
Input capacitance:
Frequency range: 15Hz to 1 MHz and d.c. respectively
NOTE - Appropriate measures should be taken to obtain the correct value in case of non-
sinusoidal waveforms.
= 0.35V(peak);
2
= 0.35V(peak) for a. c. and U
2
= 35V(peak) for a. c. correspend to the value 70 mA(peark) a. c. for
1
Measuring network for TOUCH CURRENTS
)
1M
200 pF
= 1.0V for d. c. correspond to the
1
Figure 1
2
and U
, does not
1
2
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