Acorn Computers Limited BBC A, Руководство по оборудованию, Страница: 15 / 47

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discharge is hardly worth considering recent research has proved otherwise. Recent investigations have
revealed that damage caused to MOS and CMOS integrated circuits may not be immediately apparent,
that is to say that the device may function perfectly satisfactorily but will fail after only a relatively short
time in service.
The number of MOS devices which you will be handling whilst upgrading or modifying your machine does
not warrant the expense involved in purchasing any sophisticated anti-static handling equipment but a
few simple precautions should be observed;
i) Avoid wearing any static generating materials such as Nylon.
ii) Do not have monitors or televisions switched on in close proximity to where you are working. There is
a very high electrostatic field produced in the vicinity of the screen.
iii)
Before commencing work touch some metal object that is known to be at Earth potential. The chrome
portion of a central heating radiator valve or water tap are ideal.
iv)
If possible, you should carry out the work on a conductive surface. This work surface should be
connected to the mains EARTH via a 1 Megohm resistor. Do not on any account connect the work
surface anything other than EARTH. Whilst handling the PCB's or integrated circuits keep them
positioned on the conductive surface and try to keep part of your body in contact with the surface. The
forearms are generally most easily kept in contact with the working surface.
v) Make sure that you use a low leakage soldering iron with an earthed bit. The ideal type is one which
operates via a low voltage transformer (usually 24 volts) although these tend to be rather expensive. A
mains operated iron with an earthed bit is generally suitable. The section below on soldering gives more
details on soldering irons.
vi) If at all possible you should avoid carrying out the work in warm dry atmospheres since these usually
produce high static charge levels.