Codan NGT 2010 RF Technical & Service Manual page 51

Unsoldering
When unsoldering a component, use a solder sucker or solder wick to remove solder.
CAUTION
Component substitution
Avoid unnecessary component substitution as this may damage the component, the
circuit track or adjacent components.
Component replacement
When a component is diagnosed as defective, or the fault cannot be diagnosed in any
other way than by substitution, observe the following when replacing components:
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NGT Transceiver System Technical Service Manual
Do not use sharp metal tools such as screwdrivers or twist drills to remove
components as these may damage the printed circuit track and plated thru-
holes.
Surface-mount components: The removal or replacement of surface-mount
components should only be attempted by a skilled technician experienced in
handling surface-mount components, using special tools for desoldering.
Remove solder: When a component has been unsoldered from the board, ensure the
holes are clear of solder before inserting the leads of the replacement component.
Never force the leads through the holes as this will damage the circuit
CAUTION
track, particularly where plated thru-holes are used.
Observe orientation: Before replacing defective diodes, transistors, electrolytic
capacitors or integrated circuits, observe any markings that indicate polarity or
orientation. It is essential that these types of components are installed correctly. If
necessary, consult the manufacturer's data for indications of the polarity of diodes,
capacitors and transistors.
Heatsinking: When soldering heat-sensitive components to the circuit board, where
possible use long-nosed pliers or some other form of heatsinking on the leads of the
components.
Thermal conduction: When replacing transistors that are mounted on heatsinks,
ensure there is thermal conduction between the heatsink and the component being
replaced. This can be achieved by cleaning the mounting surfaces then re-coating
them with a thermal conduction compound such as Jermyn Thermaflow A30.
Maintenance
27