Removal And Replacement Preliminaries; Electrostatic Discharge Information; Generating Static - Compaq Deskpro EX User Manual

3
chapter
R & R
EMOVAL
This chapter provides general service information for the computer. Adherence to the
procedures and precautions described in this chapter is essential for proper service.
CAUTION: When the computer is plugged into an AC power source there is always voltage applied to
the system board. You must disconnect the power cord from the power source before opening the
computer to prevent system board or component damage.
3.1

Electrostatic Discharge Information

A sudden discharge of static electricity from your finger or other conductor can destroy
static-sensitive devices or microcircuitry. Often the spark is neither felt nor heard, but
damage occurs. An electronic device exposed to electrostatic discharge (ESD) may not be
affected at all and can work perfectly throughout a normal cycle. The device may function
normally for a while, then degrade in the internal layers, reducing its life expectancy.
Networks built into many integrated circuits provide some protection, but in many cases,
the discharge contains enough power to alter device parameters or melt silicon junctions.
3.1.1

Generating Static

The following table shows that:
!
Different activities generate different amounts of static electricity.
!
Static electricity increases as humidity decreases.
Event
Walking across carpet
Walking across vinyl floor
Motions of bench worker
Removing DIPs* from plastic tube
Removing DIPs* from vinyl tray
Removing DIPs* from Styrofoam
Removing bubble pack from PCB
Packing PCBs in foam-lined box
*Dual Inline Packaging (DIP) is the packaging around individual microcircuitry.
These are then multi-packaged inside plastic tubes, trays, or Styrofoam.
700 volts can degrade a product.
EPLACEMENT
P
RELIMINARIES
Relative Humidity
55% 40%
7,500 V 15,000 V 35,000 V
3,000 V 5,000 V 12,000 V
400 V 800 V
400 V 700 V
2,000 V 4,000 V 11,500 V
3,500 V 5,000 V 14,500 V
7,000 V 20,000 V 26,500 V
5,000 V 11,000 V 21,000 V
Compaq Deskpro EX Series of Personal Computers
10%
6,000 V
2,000 V
3-1