4-2
Assembly
Access
General Safety Procedures
The following simple precautions can save a
life.
•
00
all
possible operations with the computer unplugged from the power source.
• If installation, maintenance,
or
repair must be
done
with the computer energized, take the
following precautions:
a. Never work alone
in
high -voltage areas.
In
case of accidental shock, a
life
may
depend
on
rapid removal from the energized source
and
appropriate first-aid action.
b.
Employees working
in
high-voltage areas should know where to obtain respiratory
resuscitation and/or cardiopulmonary resuscitation (CPR),
in
case a fellow worder
needs
assistance.
c.
In
case of burns, treat only after the person
is
breathing
and
has a normal heartbeat.
• If primary wiring change
is
made, perform continuity test between power cord ground
and
metal chassis. Record results
on
Repair Order.
CAUTION
THE COMPUTER HAS ASSEMBLIES AND COMPONENTS SENSI-
TIVE TO ELECTROSTATIC DISCHARGE. READ THE FOLLOWING
SECTION
AND OBSERVE THE PROCEDURES TO AVOID DAM-
AGE
TO THE COMPUTER AND ITS PARTS.
Electrostatic Discharge
Electrostatic discharge (ESO) causes failure
in
many PC assemblies, other assemblies,
and
compo-
nents. Processor stack finstrates are particularly vulnerable to ESO damage. Static electricity
doesn't
appear
to be dangerous because much of the ESO that can cause
component
or
assembly failure
is
too small to
be
felt.
Humans
can sense ESO of 3500-5000V. However, a discharge of 300V
is
enough
to destroy many components.
Assemblies
and
equipment containing ESO-sensitive parts are often as sensitive as the most sensi-
tive part they contain. Protective circuitry
in
these assemblies
and
equipment provides varying
degrees of protection from
ESO applied to their terminals.
Such
assemblies
and
equipment, howev-
er, are
still
vulnerable to induced ESO caused by strong electrostatic fields
or
by contact of electrical
connections
or
paths with a charged object.
Static
damage
is
not always catastrophic. Sometimes a part slowly degrades, resulting in deteriorat-
ing performance. For example, internal resistance changes cause
speed
or
voltage changes. Results
include intermittent
or
latchup problems (for example, a line printer prints
bad
data).
When
disassembling the computer, a portable conductive field service antistatic
kit
should
be
used
to eliminate ESO when handling
or
temporarily setting aside ESO-sensitive parts. The
kit
contains a
wrist strap, antistatic mat,
and
grounding cable.
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