Acorn Computers Limited BBC A, Руководство по оборудованию, Страница: 14 / 47

14
It is important to allow yourself plenty of time in which to carry out the work. Do not be tempted to rush
because this usually results in poor quality workmanship. Also if you rush work of this type it is very likely
that mistakes will be made and these could turn out to be costly.
A systematic and orderly approach should be adopted since this will minimise the likelihood of doing
something incorrectly or omitting something. In practise this will mean planning ahead by mentally going
through the procedure before you commence work. Try to keep the workbench tidy and do not clutter the
space up with unnecessary objects, leave yourself plenty of room in which to work.
It is also important to seat yourself in a comfortable position at the workbench. If you are not comfortable
whilst you are carrying out the work you will be tempted to rush the job and hence run a higher risk of
making mistakes. If you do rush the work the end result will probably not be of a good standard.
Make sure that you have plenty of light on the work area, a strong light will make most of the work that
you will be carrying out on the machine far easier.
Once you have completed the work on the printed circuit boards it is essential that you conduct a detailed
visual inspection of both the work which you have carried out and the remaining areas of the PCB. It is
quite likely that small pieces of wire etc., will have fallen onto the PCB whilst you were working on it.
Under no circumstances should you reassemble and switch on the machine without having carried out
this inspection, in fact it is advisable to inspect the board at least twice using a strong light and an
eyeglass. As mentioned in chapter 5, be sure to check that the heat sink on IC6 (Video Uncommitted
Logic Array) is firmly seated and that non of the resistors and capacitors have become bent over and
shorted. The importance of this inspection cannot be over emphasised.
2.2 Anti-Static Precautions.
Many of the integrated circuits used within the BBC Microcomputer are either Negative Metal Oxide
Semiconductor (NMOS) or Complementary Metal Oxide Semiconductor (CMOS) types. These types of
IC's are susceptible to damage by static discharge and special precautions are, therefore, necessary
when handling these devices.
Opinions on exactly what precautions should be observed when handling the devices seem to differ but
the procedures outlined below, if observed, will ensure that the risk of damage to the IC's is very minimal.
Although many people believe that with present day MOS devices the possibly of damage due to static