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Removal and Replacement Preliminaries and
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
Ä
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 table below shows how different activities generate static electricity at different electrostatic
voltage levels.
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.
Compaq Prosignia Desktop 340 Series Computer
Typical Electrostatic Voltages
Routine Care
Relative Humidity
10%
40%
35,000 V
15,000 V
12,000 V
5,000 V
6,000 V
800 V
2,000 V
700 V
11,500 V
4,000 V
14,500 V
5,000 V
26,500 V
20,000 V
21,000 V
11,000 V
3
55%
7,500 V
3,000 V
400 V
400 V
2,000 V
3,500 V
7,000 V
5,000 V
3–1
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