Barrett 900 Series, Technical Manual

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BARRETT 900 SERIES TRANSCEIVERS
5.0 Maintenance
5.1 Introduction
5.2 Printed Circuit Board (PCB) maintenance
5.3 Component replacement
This section provides maintenance and fault finding procedures that can be carried out on Barrett 900 series
transceivers.
Barrett 900 series transceivers use four layer PCB's for the microprocessor and RF/Audio sections and two
layer PCB's, for the PA , front panel and remote head. 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 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 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.
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 900 series transceivers. It is
essential that surface mount work stations be used for removal and replacement of these components.
Note that there are some capacitors on the Microprocessor board which require special low temperature
solder and soldering equipment. These capacitors can be recognized by their silvery appearance. They are
C8, C9, C34, C35, C194, C173.
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