HP 27140A Hardware Reference Manual page 5

Servicing
General
' 1 i"' H ,[e)
I
Caution
I
Any servicing, adjustment, maintenance, or repair of this product must
be performed only by qualified personnel.
SAFE'lY
EARm
GROUND - The computer on which this product is
installed is a safety class I product and is provided with a protective
earthing terminal. An un interruptible safety ground must be provided
from the main source to the product input wiring terminals, power cord,
or supplied power cord set. Whenever it is likely that the protection has
been impaired, the product must be made inoperative and must be
secured against any unintended operation.
STATIC SENSmVE DEVICES
When any two materials make contact, their surfaces are crushed on the
atomic level and electrons pass back and forth between the objects. On
separation, one surface comes away with excess electrons (negatively
charged) while the other is electron deficient (positively charged). The
level of charge that is developed depends on the
type
of material. In-
sulators can easily build up charges in excess of 20,000 volts. A person
working at a bench or walking across a floor can build up a charge of
many thousands of volts. The amount of static voltage developed depends
on the rate of generation of the charge and the capacitance of the body
holding the charge. If the discharge happens to go throUgh a semiconduc-
tor device and the transient current pulse is not effectively diverted by
protection circuitry, the resulting current flow through the device can raise
the temperature of internal junctions to their melting points .. MOS struc-
tures are also susceptible to dieletric damage due to high fields.
The
resulting damage can range from complete destruction to latent degrada-
tion.
Small geometry semiconductor devices are especially susceptible to
damage by static discharge.
The MUX card is shipped in a transparent static shielding bag. The card
should be kept in this bag at all times until it is installed in the system.
Save this bag for storing or transporting the card. When installing the
card in the system, do not touch any components. Hold the card only by
its edges or extractor levers.
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