HP Desktop Pro A G2, Руководство по техническому обслуживанию и ремонту

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3 Routine care, SATA drive guidelines, 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 the following about static electricity:
● 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
Removing DIPs from vinyl tray
Removing DIPs from Styrofoam
Removing bubble pack from PCB
Packing PCBs in foam-lined box
2,000 V
3,500 V
7,000 V
5,000 V
4,000 V
5,000 V
20,000 V
11,000 V
11,500 V
14,500 V
26,500 V
21,000 V
NOTE: 700 volts is enough to degrade a product.
8 Chapter 3 Routine care, SATA drive guidelines, and disassembly preparation