Servicing Precautions - Nokia 920C Service Manual

1 Precautions

1-2 Servicing Precautions

WARNING1: First read the "Safety Precautions" section of this manual. If unforeseen circumstances
create conflict between the servicing precautions and safety precautions, always
follow the safety precautions.
WARNING2: A high voltage VR replaced in the wrong direction may cause excessive X-ray
emissions.
WARNING3: An electrolytic capacitor installed with the wrong polarity might explode.
1. Servicing precautions are printed on the cabinet,
and should be followed closely.
2. Always unplug the unitÕs AC power cord from the
AC power source before attempting to: (a) remove
or reinstall any component or assembly, (b)
disconnect PCB plugs or connectors, (c) connect all
test components in parallel with an electrolytic
capacitor.
3. Some components are raised above the printed
circuit board for safety. An insulation tube or tape
is sometimes used. The internal wiring is
sometimes clamped to prevent contact with
thermally hot components. Reinstall all such
elements to their original position.
4. After servicing, always check that the screws,
components and wiring have been correctly
reinstalled. Make sure that the area around the
serviced part has not been damaged.
1-3 Electrostatically Sensitive Devices (ESD) Precautions
Some semiconductor (solid state) devices can be easily damaged by static electricity. Such components are commonly
called Electrostatically Sensitive Devices (ESD). Examples of typical ESD devices are integrated circuits and some field-
effect transistors. The following techniques will reduce the incidence of component damage caused by static electricity.
1. Immediately before handling any semiconductor
components or assemblies, drain the electrostatic
charge from your body by touching a known earth
ground. Alternatively, wear a discharging wrist-
strap device. To avoid a shock hazard, be sure to
remove the wrist strap before applying power to
the monitor.
2. After removing an ESD-equipped assembly, place it
on a conductive surface such as aluminum foil to
prevent accumulation of an electrostatic charge.
3. Do not use freon-propelled chemicals. These can
generate electrical charges sufficient to damage
ESDs.
4. Use only a grounded-tip soldering iron to solder or
desolder ESDs.
5. Use only an anti-static solder removal device. Some
solder removal devices not classified as Òanti-staticÓ
can generate electrical charges sufficient to damage
ESDs.
1-2
5. Check the insulation between the blades of the AC
plug and accessible conductive parts (examples:
metal panels, input terminals and earphone jacks).
6. Insulation Checking Procedure: Disconnect the
power cord from the AC source and turn the power
switch ON. Connect an insulation resistance meter
(500 V) to the blades of the AC plug.
The insulation resistance between each blade of the
AC plug and accessible conductive parts (see
above) should be greater than 1 megohm.
7. Never defeat any of the +B voltage interlocks. Do
not apply AC power to the unit (or any of its
assemblies) unless all solid-state heat sinks are
correctly installed.
8. Always connect a test instrumentÕs ground lead to
the instrument chassis ground before connecting the
positive lead; always remove the instrumentÕs
ground lead last.
6. Do not remove a replacement ESD from its
protective package until you are ready to install it.
Most replacement ESDs are packaged with leads
that are electrically shorted together by conductive
foam, aluminum foil or other conductive materials.
7. Immediately before removing the protective
material from the leads of a replacement ESD,
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
other safety precautions.
8. Minimize body motions when handling
unpackaged replacement ESDs. Motions such as
brushing clothes together, or lifting your foot from
a carpeted floor can generate enough static
electricity to damage an ESD.
9. Indicates ESDs on the Schematic Diagram in
this manual.
720C/920C