4230 Flow Meter
Section 5 Maintenance and Service
5-16
• Never perform any work in a room with a carpeted floor.
• Always roll up your sleeves so that your arms are in
contact with the working surface.
• Avoid using a work surface made of an extremely good
insulator.
Plastic or glass are good insulators and should be
avoided. A metal surface is best; a wood surface is
acceptable. Conductive grounding mats are available for
work stations and are worthwhile if much repair is to be
done.
• The degree of hazard depends on the level of humidity.
Be particularly careful if the work area is extremely dry,
or if the work is being done in the winter, when indoor
forced heating and outdoor low temperatures cause the
relative humidity level to be very low.
• Keep yourself grounded when handling disassembled
equipment.
When arriving at the work area, after a unit has been
opened for repair, make an effort to always be touching
the metal chassis before touching any of the circuit
components.
• Be especially careful handling the CMOS integrated
circuits when they are removed from the rest of the
circuitry.
Simply being connected to the rest of the circuitry
provides some protection. Most of the circuitry is
well-protected from damage caused by static discharge
when the unit is powered up. However, an IC should
never be replaced when the unit is turned on.
• Individual CMOS semiconductors and built-up printed
circuit boards should always be transported in
conductive packaging.
Foil is satisfactory; metallized plastic bags are also
available and work well. Ordinary plastic bags and pink
poly are not satisfactory unless the legs or leads are also
stuck into a block of black conductive foam. If
replacement components that are purchased do not
come in marked, protective packaging, do not use them.
They may already be destroyed.
• Once assembled and soldered, printed circuit boards are
easily damaged by improper repair procedures.
Do not attempt to remove components, particularly ICs,
from printed circuit boards unless skilled at this
procedure. A defective component may be located,
changed, and the unit still not work, if excessive heat or
pressure has broken the foil traces or pulled the cores
from holes on the board.
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