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Printed Circuit Board (PCB) maintenance
Barrett 2000 series transceivers use a four layer PCB for the Microprocessor/ RF/Audio section and control
head and two layer PCB’s for the PA and transition PCB’s.
When working on these PCB’s observe the following precautions:-
Excessive heat could lift a track from the circuit boards, resulting in serious damage. Avoid the use of high-
powered soldering irons. A soldering iron rated at a maximum of 60W and temperature controlled to
approximately 370 degrees C is suitable for most tasks. For removal or installation of heavier components
such as PA transistors and main power leads a soldering iron rated at a higher temperature of 425 degrees
C is required. When unsoldering, use a solder-sucker or Solder wick to remove the solder.
Burned or broken sections of printed circuit track may be repaired by bridging the damaged section with
tinned copper wire. Care must be taken to remove the PCB solder mask covering the track either side of
the burn or break to allow it to be tinned before making the repair. Also in the case of a burn, the fibreglass
area that has been burnt must be cleaned to remove any carbon deposits.
Component replacement
When replacing defective diodes, transistors, electrolytic Capacitors or integrated circuits, observe any
marking that indicate polarity or orientation. It is essential that these types of components are installed
correctly.
Components with leads that are soldered into plated through holes in the PCB such as integrated circuits,
diodes, resistors and Capacitors, can often be replaced with the minimum of risk by clipping its leads as
close to the component as possible. The leads left in the PCB can then be removed by carefully heating
the solder joint on each remaining lead individually, then carefully withdrawing the lead from the PCB using
a pair of pliers. Avoid pulling on the lead before the solder has fully melted around the lead as damage to
plated through holes or layers of the PCB may occur. Once the component has been removed use solder
wick or a solder sucker to clear the remaining solder from the hole.
When replacing heat sensitive components to the circuit board, if possible use long-nosed pliers or similar
to conduct heat away from the component.
When replacing PA output transistors and drivers ensure that the thermal conduction paste between the
heatsink and the component is replaced. This can be achieved by cleaning the mounting surfaces, and re-
coating them with a thermal conduction compound. Only use a small amount of thermal compound but
enough to make a light cover on the surface.
Extensive use of surface mounted components is made on all PCB's in 2000 series transceivers. It is
essential that surface mount work stations be used for removal and replacement of these components.
CMOS devices
A number of Complementary Metal Oxide Semiconductor (CMOS) devices are used in the transceiver and
most of them have built-in protection. However, their extremely high open-circuit impedance makes them
susceptible to damage from static charges. Care must be used when handling these devices during
servicing. By observing the following precautions, the risk of damage to CMOS devices will be minimised:-
Replacement CMOS devices are supplied in special conductive packaging. They should remain in this
packaging until required for use.
Ensure that power supplies are switched off before making connection or disconnections between circuit
boards.
Handle circuit boards or touch conductive parts as little as possible.
Anything connected to or touching the circuit board tracks should be grounded.
