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4 Safety Precautions
4.1 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.
(This "Safety Precaution" is applied only in U.S.A.)
1.
Before servicing, unplug the power cord to prevent an electric shock.
2.
When replacing parts, use only manufacturer's recommended components for safety.
3.
Check the condition of the power cord. Replace if wear or damage is evident.
4.
After servicing, be sure to restore the lead dress, insulation barriers, insulation papers, shields, etc.
5.
Before returning the serviced equipment to the customer, be sure to make the following insulation resistance test
to prevent the customer from being exposed to a shock hazard.
4.1.1 Leakage Current Cold Check
1.
Unplug the AC cord and connect a jumper between the two prongs on the plug.
2.
Measure the resistance value, with an ohmmeter, between the jumpered AC plug and each exposed metallic
cabinet part on the equipment such as screwheads, connectors, control shafts, etc. When the exposed metallic
part has a return path to the chassis, the reading should be between 1MΩ and 5.2MΩ.
When the exposed metal does not have a return path to the chassis, the reading must be
4.1.2 Leakage Current Hot Check (See Figure 1)
1.
Plug the AC cord directly into the AC outlet. Do not use an isolation transformer for this check.
2.
Connect a 1.5kΩ, 10 watts resistor, in parallel with a 0.15µF capacitor, 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 an AC voltmeter, with 1000 ohms/volt 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 0.75 volts RMS. A leakage current tester (Simpson Model 229 or
equivalent) may be used to make the hot checks, leakage current must not exceed 1/2 milliamp. 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.
4.1.3 Caution for fuse replacement
Fig. 1
.
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