General Safety Procedures; Electrostatic Discharge - HP 9020 Service Manual

4-2
Assembly Access
WARNING
UNPLUG COMPUTER POWER CORD FROM AC OUTLET BEFORE
REMOVING ANY ASSEMBLY.
LETHAL VOLTAGES ARE PRESENT INSIDE THE COMPUTER.
OBSERVE ALL WARNINGS IN THIS MANUAL, AND OBSERVE
THE FOLLOWING SAFETY PROCEDURES.
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 worker 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 a minimum ESO of 3500-5000V. However, a discharge of
300V is enough to destroy some 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.