Grass Valley SMS-6000 Series - Manual (Page 115)

5-11
Replacing Parts
Replacing Parts
If a part is to be replaced then a qualified technician should perform the
work. The printed circuit boards in this equipment frequently use trace
widths of 0.012 in. which can easily be damaged if proper care is not taken.
Also many of the devices are sensitive to static and precautions should be
taken to minimize such risks. Work on circuit board modules should be
undertaken on conductive rubber mats to avoid physical and static
damage.
Most integrated circuits are not socketed, except for devices which might
require replacement during the life of the equipment (such as EPROMs).
The reason for this is two fold. Firstly, in the signal path sockets can
degrade the HF performance in the video circuitry. Secondly, sockets
contribute to product unreliability: they are an extra component in the
chain and are generally less reliable than the chips whose replacement they
are intended to facilitate.
If a chip or other component has to be replaced the leads should be cut off
with fine cutters on the component side. The leads can then be heated with
a soldering iron and removed one at a time. Remove excess solder with
solder wick or solder sucker until the hole is clear. Alternatively, the use of
special pumped de-soldering stations is strongly recommended.
If the new component is an IC then a socket should normally be used as the
risk of damage to the traces of the circuit board would increase rapidly if it
were to be replaced again in the future, outweighing the inherent risks of
the socket itself. The exception to this rule is if in the video path the
component is removed very cleanly and the pads at the holes look in good
condition then the chip may be fitted and soldered in place. Otherwise it is
better to use a socket and tolerate the small degradation in performance
that might result.
When removing a component such as EPROM from a socket pull it out
straight and evenly a little at a time to avoid bending the leads. A small flat
bladed screwdriver is an excellent tool for this task.
When placing a component in a socket ensure that the leads are straight
and that they are all lined up in the socket before pushing it in evenly and
firmly. If the leads of a chip have become badly bent they may fracture
when they are straightened. In this case the device must be replaced with
a new one.
Devices in large square sockets (PLCC sockets) can only be removed with
a special tool. Do not attempt to remove devices without this tool as you
may damage the socket which would be difficult to replace without
damaging the circuit board.