HP 500B - Manual (Page 98)

E Routine Care and Disassembly
Preparation
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, voltage is always 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.
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 appear to be affected at all and
can work perfectly throughout a normal cycle. The device may function normally for a while, but it has
been degraded 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.
Generating Static
The following table shows that:
● Different activities generate different amounts of static electricity.
● Static electricity increases as humidity decreases.
Relative Humidity
Event 55% 40% 10%
Walking across carpet
Walking across vinyl floor
Motions of bench worker
Removing DIPs* from plastic tube
7,500 V
3,000 V
400 V
400 V
15,000 V
5,000 V
800 V
700 V
35,000 V
12,000 V
6,000 V
2,000 V
90 Appendix E Routine Care and Disassembly Preparation