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1 Safety Precautions
1.1.
General Guidelines
1. When conducting repairs and servicing, do not attempt to modify the equipment, its parts or its materials.
2. When wiring units (with cables, flexible cables or lead wires) are supplied as repair parts and only one wire or some of the
wires have been broken or disconnected, do not attempt to repair or re-wire the units. Replace the entire wiring unit instead.
3. When conducting repairs and servicing, do not twist the Fasten connectors but plug them straight in or unplug them straight
out.
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.
1.1.1.
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 1Mohm and 5.2Mohm.
When the exposed metal does not have a return path to
the chassis, the reading must be
1.1.2.
1. Plug the AC cord directly into the AC outlet. Do not use
2. Connect a 1.5kohm, 10 watts resistor, in parallel with a
3. Use an AC voltmeter, with 1000 ohms/volt or more
.
4. Check each exposed metallic part, and measure the
5. Reverse the AC plug in the AC outlet and repeat each of
6. The potential at any point should not exceed 0.75 volts
3
Leakage Current Hot Check (See
Figure 1.)
an isolation transformer for this check.
0.15μF capacitors, between each exposed metallic part
on the set and a good earth ground such as a water pipe,
as shown in Figure 1.
sensitivity, to measure the potential across the resistor.
voltage at each point.
the above measurements.
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 outside 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.
Figure 1
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