Compaq 340 Series manual Removal and Replacement Preliminaries and Routine Care, Generating Static

3

Removal and Replacement Preliminaries and Routine Care

This chapter provides general service information for the computer. Adherence to the procedures and precautions described in this chapter is essential for proper service.

ÄCAUTION: 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.

3.1Electrostatic 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.

Typical Electrostatic Voltages

		Relative Humidity
Event	10%		40%		55%
Walking across carpet	35,000	V	15,000	V	7,500	V
Walking across vinyl floor	12,000	V	5,000	V	3,000	V
Motions of bench worker	6,000	V	800	V	400	V
Removing DIPs* from plastic tube	2,000	V	700	V	400	V
Removing DIPs* from vinyl tray	11,500	V	4,000	V	2,000	V
Removing DIPs* from Styrofoam	14,500	V	5,000	V	3,500	V
Removing bubble pack from PCB	26,500	V	20,000	V	7,000	V
Packing PCBs in foam-lined box	21,000	V	11,000	V	5,000	V

*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 3–1