Servicing Precautions; General Servicing Precautions; Insulation Checking Procedure; Electrostatically Sensitive (Es) Devices - Zenith DVD5201 Service Manual

SERVICING PRECAUTIONS

Before servicing the DVD covered by this service data
(and its supplements and addendums), read and follow
the safety precautions. If unforeseen circumstances create
conflict between the following servicing precautions and
any of the safety precautions in this publication, always
follow the safety precautions. Remember, safety first.

GENERAL SERVICING PRECAUTIONS

1) Always unplug the DVD AC power cord from the AC
power source before:
a) Removing or reinstalling any component, circuit
board, module, or any other assembly.
b) Disconnection or reconnecting any internal elec-
trical plug or other electrical connection.
c) Connecting a test substitute in parallel with an elec-
trolytic capacitor.
Caution: A wrong part substitution or incorrect polarity
installation of electrolytic capacitors may result in
an explosion hazard.
2) Do not spray chemicals on or near this DVD or any of
its assemblies.
3) Unless specified otherwise in this service data, clean
electrical contacts by applying an appropriate con-
tact cleaning solution to the contacts with a pipe
cleaner, cotton-tipped swab, or comparable soft ap-
plicator. Unless specified otherwise in this service
data, lubrication of contacts is not required.
4) Do not defeat any plug/socket B+ voltage interlocks
with which instruments covered by this service manual
might be equipped.
5) Do not apply AC power to this DVD and/or any of its
electrical assemblies unless all solid-state device heat
sinks are correctly installed.
6) Always connect test instrument ground lead to the
appropriate ground before connection the test in-
strument positive lead. Always remove the test in-
strument ground lead last.

INSULATION CHECKING PROCEDURE

Disconnect the attachment plug from the AC outlet and
turn the power on. Connect an insulation resistance meter
(500V) to the blades of the attachment plug. The
insulation resistance between each blade of the
attachment plug and accessible conductive parts should
be more than 1M-ohm. Accessible Conductive Parts
VR166 - 923-03461
SERVICING
including Metal pan-els, Input terminals, Earphone jacks,
etc.

ELECTROSTATICALLY SENSITIVE (ES) DEVICES

Some semiconductor (solid state) devices can be
damaged easily by static electricity. Such components
commonly 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 touch-
ing a known earth ground. Alternatively, obtain and
wear a commercially available discharging wrist strap
device, which should be removed 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 sur-
face 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
unsolder ES devices.
4) Use only an anti-static solder removal device. Some
solder removal devices not classified a "anti-static"
can generate electrical charges sufficient to damage
ES devices.
5) Do not use freon-propelled chemicals. These can gen-
erate electrical charge sufficient to damage ES de-
vices.
6) Do not remove a replacement ES device from its pro-
tective package until immediately before you are ready
to install it. (Most replacement ES devices are pack-
aged with leads electrically shorted together by con-
ductive foam, aluminum foil, or comparable conduc-
tive material).
7) Immediately before removing the protective material
from the leads of a 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 other safety precautions.
8) Minimize bodily motions when handling unpackaged
replacement ES devices. (Normally harmless motion such
as the brushing together of your clothes fabric or the
lifting of your foot from a carpeted floor can gener-
ate static electricity sufficient to damage an ES de-
vice.)
7
DVD2 - SERVICING