Sencore POWERITE PR57 User Manual

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 kΩ and
5.2 MΩ.
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 kΩ, 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.

Sencore POWERITE PR57 Specifications

General

Brand	Sencore
Model	POWERITE PR57
Category	Test Equipment
Language	English

Summary

Servicing Hot Chassis and Performing the Leakage Test

What is the Leakage Test?

Explains the safety check to prevent customer shocks from exposed metal parts on AC-powered devices.

Why Don't More Servicers Perform the Leakage Test?

Highlights that technicians avoid the test due to complexity, setup time, and required parts.

Leakage Current Cold Check

Details how to measure resistance between AC plug and exposed metal parts when the unit is unplugged.

Leakage Current Hot Check

Explains measuring voltage across a resistor connected to exposed metal and earth ground while the unit is powered.

Why You Should Perform the Leakage Test

Why Should You Perform the Leakage Test?

Emphasizes that even one leaky chassis can lead to costly damage, lawsuits, and customer harm.

Causes of Leakage

Shorted Antenna Bypass Capacitors

Explains how shorted bypass capacitors can expose antenna terminals to AC voltage.

Improperly Installed Tuner

Discusses how incorrect tuner installation can tie the AC line to exposed metal parts.

Conductive Knobs

Warns that metal or chrome-plated knobs can conduct current from a hot chassis.

Defective Isolation Transformers

Notes that leakage in isolation transformers can cause the entire chassis to become hot.

AC Bypass Capacitors

Describes how failed AC bypass capacitors can create a direct connection between the AC line and chassis.

Bent Rabbit Ears

Explains how bent rabbit ears can touch a hot chassis, energizing the antenna terminals.

Improper Installation of Parts

Mentions forgetting insulating parts like "fish paper" can create a hazard.

Foreign Objects Touching the AC Line

Warns about wires or solder falling onto AC line components.

A Broken Safety Ground

Indicates a broken ground can cause controls to "float" at line voltage.

Using Long Metal Screws

States long screws can penetrate mounting tabs and touch the metal chassis.

Adding An Earphone

Highlights the shock hazard of connecting earphones to un-isolated sets.

Foreign Objects

Mentions metal objects like coins or hairpins falling inside the set can cause a shock hazard.

Connecting an External Speaker

Warns about wiring accessories to sets without isolation transformers.

The PR57 Leakage Test

The PR57 Leakage Test: It's Fast and Simple

Explains the PR57 simplifies the test by referencing all circuits to its isolated output.

Performing the Leakage Test with the PR57

Provides a step-by-step guide on how to conduct the leakage test using the PR57.

Leakage Limits and Calibration

How Much Leakage is Bad?

Discusses the effects of electrical shock and safe leakage current limits.

Measuring Leakage at Lower Levels

Explains measuring very low leakage (10-100 microamps) for medical or hospital equipment.

Checking the Calibration of the Leakage Test

Details how to verify the PR57's leakage test calibration using its built-in resistor.

Testing Leakage on Three-Wire Units

Explains how the PR57 test works on units with grounded AC cords, maintaining chassis at earth potential.

Testing for Line Cord and Extension Cord Leakage

Covers testing line and extension cords for leakage, which can cause fires.