manufacturer’s specified parts to prevent shock, fire, or other hazards.
Do not modify the original design without permission of manufacturer.
2. An Isolation Transformer should always be used during the servicing
of AC Adaptor whose chassis is not isolated from the AC power line.
Use a transformer of adequate power rating as this protects the
technician from accidents resulting in personalinjury from electrical
shocks. It will also protect AC Adaptor from being damaged by
accidental shorting that may occur during servicing.
3. 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.
4. After servicing, see to it that all the protective devices such as
insulation barriers, insulation papers shields are properly installed.
5. After servicing, make the following leakage current checks to prevent
the customer from being exposed to shock hazards.
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 thechassis, the reading
should be between 1 M and 5.2 M . When the exposed metal does
not have a return path to the chassis, the reading must be infinity.
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 1.5 k , 10 W resistor, in parallel with a 0.15 F capacitor,
between each exposed metallic part on the set and a good earth
ground, as shown in Figure 1.
3. Use an AC voltmeter, with 1 k /V 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
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