Safety Precautions - Panasonic AG-7350 Series Service Manual

SAFElY PRECAUTIONS
GENERAL GUIDEUNES
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.
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 ohm meter, be-
tween the jumpered AC plug and each exposed metallic
cabinet part on the equipment such as screwheads con-
nectors, control shafts,etc. When the exposed metallic
part has a return path to the chassis, the reading should
be between 1M ohm and 5.2 M ohm.
When the exposed metal does not have a return path to
the chassis, the reading must be oo.
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 1.5k ohm, 10 watts resistor, In parallel with a
0.15uF 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 sen-
sitivity, 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 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
equivalent) may be used to make the hot checks, leak-
age 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.
AC VOLTMETER
Hot-Check Circuit
Figure 1
- 2 -
ELECTROSTATICALLY
SENSITIVE (ES) DEVICES
Some semiconductor (solid state) devices can be dam-
aged easily by static electricity. Such components com-
monly are called Electrostatically Sensitive (ES) Devices.
Examples of typical ES devices are integrated circuits and
some field-effect transistors and semiconductor chip
components. The following techniques should be used to
help reduce the incidence of component damage caused
by static electricity.
1 . Immediately before handling any semiconductor com-
ponent or semiconductor-equipped assembly, drain off
any electrostatic charge on your body by touching a
known earth ground.
Alternatively, obtain and wear a commercially available
discharging wrist strap device, which should be re-
moved for potential shock reasons prior to applying
power to the unit under test.
2. After removing an electrical assembly equipped with ES
devices, place the assembly on a conductive surface
such as aluminum foil, to prevent electrostatic charge
buildup or exposure of the assembly.
3. Use only a grounded-tip soldering Iron to solder or un-
solder ES devices.
4. Use only an anti-static solder removal device classified
as anti-static can generate electrical charges sufficient
to damage ES devices.
5. Do not use freon-propelled chemicals. These can gener-
ate electrical charges sufficient to damage ES devices.
6. Do not remove a replacement ES device from its protec-
tive package untilimmedlately before you are ready to
Install it. (Most replacementES devices are packaged
with leads eletcrically shorted together by conductive
foam, aluminum foil or comparable conductive mate-
rial).
7. Immediately before removing the protective materia!
from the leads of replacement ES device, touch the
protective material to the chassis or circuit assembly Into
which the device will be installed.
CAUTION : Be sure no power Is applied to the chassis or
circuit, and observe all otner asfety precautions.
8. Minimize bodily motions when handling unpackaged
replacement ES devices. (Otherwise harmless motion
such as the brushing together of your clothes fabric or
the lifting of your foot from a carpeted floor can generate
static electricity sufficient to damage an ES device).