LBI-33057
17
SURFACE MOUNTED INTEGRATED
CIRCUIT REPLACEMENT
Surface mounted IC soldering and de-soldering
techniques are similar to the above outlined procedures
for the surface mounted chip components. Use extreme
care and observe static precautions when removing or
replacing a defective (or suspect) IC. This will prevent
any damage to the printed wire board or the surround-
ing circuitry.
Replacement of a surface mounted IC is best com-
pleted using a hot-air soldering system. The IC can easily
be removed and installed using hot air. See the manufac-
turers instructions for complete details on tip selection
and other operating instructions unique to your system.
If a hot-air system is not available, the service tech-
nician may wish to clip the pins near the body of the de-
fective IC and remove it. The pins can then be removed
from the PWB with a standard soldering iron and tweez-
ers and then the new IC can be installed. It should not be
necessary to tin any of the IC pins before the installation
process.
The "chip-on-board" ICs used in the radio cannot be
replaced. Failure of this type of IC will require board re-
placement.
MODULE REPLACEMENT
The modules, all of which are located on the RF
Board, are very reliable devices. Before replacing any of
the modules, check the associated circuitry thoroughly to
insure there is not a problem elsewhere. If replacement is
necessary, follow the below procedures.
All of the component lead holes for the modules on
the RF Board are plated through from the top to the bot-
tom of the board. This allows for easy removal and re-
placement of the modules as long as appropriate solder-
ing techniques are observed. Always observe static pre-
cautions when handling the board.
To remove the PA module, it is first necessary to re-
move the hardware which supports it. Two (2) Torx
screws and a support bracket secure the module to the
eggcrate casting. Two (2) Torx screws also secure the
VCO to the board.
To remove a module, position the RF Board in a
work (face down, chip components up) and remove the
solder from the plated-through points at the appropriate
pins. If a hot-air system is employed, use an appropriate
tip that will localize the heat on the pins and not on sur-
rounding chip components. Solderwick
or a vacuum
de-soldering iron will also remove the solder if a hot-air
station is not available. When all solder has been re-
moved or liquefied, the module should drop out of the
eggcrate casting.
To install a module, clean any solder from the
plated- through holes and clean all flux from the board.
Next, install the replacement module making sure that all
pins align in the proper holes. Resolder the pins to the
board. Clean the flux from the board using an approved
solvent. Clip any excess lead length.
WEATHERPROOF INTEGRITY
The M-PA radio is designed to meet the MIL-810C
& D environmental specifications. The internal circuitry
is protected from moisture by appropriate seals. Rear
Cover Assembly seals include the Front/Rear Cover As-
sembly gasket and the antenna insert gaskets. Front
Cover Assembly seals include the speaker/microphone
seal, the battery plate seal, and the volume and channel
control seals. The UDC/Monitor Button/PTT Assembly is
also designed to seal out moisture.
These seals should be inspected during any disas-
sembly/reassembly process for cracks and tears. A defec-
tive seal warrants replacement. See the Mechanical Parts
breakdown drawings and the Parts Lists for locations and
part numbers for these seals. When installing a new seal,
make sure it is seated properly before reassembly.
BATTERY PACKS
Battery packs available for use with the radio include
high and extra high capacity rechargeable units. All of
the rechargeable battery packs are factory sealed and are
not field serviceable other than properly charging them
and cleaning the contacts. Figure 8 outlines a typical
battery pack.
Radio contacts located on the top of the pack include
switched power, ground, the speaker enabling (shorting)
contacts and a continuous power contact. Four (4)
charging contacts are located on the rear side of the bat-
tery pack. These contacts provide connections to the slip-
in type chargers or vehicular chargers/repeaters while the
battery pack is still connected to the unit. The battery
charging contacts are diode protected from external
shorts.
