Removal And Replacement Prelinimaries; Electrostatic Discharge Information; Generating Static - Compaq Deskpro 2000 Maintenance & Service Manual

chapter 4
R
EMOVAL AND
P
RELIMINARIES
This chapter provides general service information for the computer. Adherence to the procedures and
precautions described in this chapter is essential for proper service.

4.1 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.
4.1.1

Generating Static

Table 4-1 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.
R
EPLACEMENT
Table 4-1
Typical Electrostatic Voltages
10%
35,000 V
12,000 V
6,000 V
2,000 V
11,500 V
14,500 V
26,500 V
21,000 V
Relative Humidity
40%
15,000 V
5,000 V
800 V
700 V
4,000 V
5,000 V
20,000 V
11,000 V
Compaq Deskpro 2000 Series of Personal Computers
55%
7,500 V
3,000 V
400 V
400 V
2,000 V
3,500 V
7,000 V
5,000 V
4-1