Servicing Hot Chassis and Performing the Leakage Test with Your
PR57 “POWERITE”®
The PR57 “POWERITE” provides a very
fast and accurate check of AC leakage
between the AC line and the exposed
metal on an AC-operated device. This
Tech Tip explains this patented leakage
test, why and when it should be
performed, and some extra applications
where it could come in handy.
What is the Leakage Test?
The leakage test assures that the TV set
or other electronic device being returned
to the customer does not have any
exposed metal parts that could give the
customer an electrical shock. Virtually all
service literature lists a safety leakage
test similar to the one shown in figure 1.
This safety check applies to all consumer
units that are connected to the AC line,
but it is most important when the device
does not have an isolation transformer.
The potential of a shock hazard increases
dramatically when the set has a hot
chassis.
Why Don’t More Servicers Perform
the Leakage Test?
Simply stated, many technicians to not
perform the safety leakage test, because
the test is complicated. It requires a good
ground, a resistor/ capacitor combination
“made up” or located among the shop
parts, and the test setup takes time.
Time is something most technicians don’t
have.
Why Should You Perform the
Leakage Test?
Even though you may find leakage on
only one chassis out of a hundred, that’s
Leakage Current Cold Check
1. Unplug the AC cord and connect a jumper between the two prongs on the plug.
2. Turn on the receiver’s power switch.
3. Measure the resistance value, with an ohmmeter, between the jumpered AC
plug and each exposed metallic cabinet part on the receiver, such as
screwheads, connectors, control shafts, etc. When the exposed metallic part
has a return path to the chassis, the reading should be between 240 k
Ω
and
5.2 M
Ω
.
When the exposed metal does not have a return path to the chassis, the reading
must be infinite.
Leakage Current Hot Check
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
Ω
, 10 watt resistor, in parallel with a 0.15 µF capacitor, between
each exposed metallic part on the set and a good earth ground such as a water
pipe.
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 ½ milliamps. In case a measurement is out-
side of the limits specified, there is a possibility of a shock hazard, and the
receiver should be repaired and rechecked before it is returned to the customer.
Fig. 1: Manufacturers include the leakage test in service literature, because
it helps them meet their legal obligation to deliver safe products to the
consumer.
