Motorola MTX Series Service Manual page 37

(215 degrees C) 445 degrees F (230
degrees C) maximum. Apply solder paste
to the exposed solder pads under the PA.
Place the circuit board in the circuit board
holder, and position the RF PA under the
heat-focus head. Lower the heat-focus
head until it is approximately 1/8"-1/4"
(0.3cm-0.6cm) above the PA cover. Turn
on the heater and begin the reflow cycle.
Heating time should not be less than two
minutes.
Once the part has reflowed, before trying to
remove the PA, carefully lower the circuit
board holder as follows:
• Loosen the thumbscrew on the shaft of
the circuit board holder,
• push the spring-loaded holder down and
away from the heat-focus head, and
• retighten the thumbscrew with the holder
in the bottomed position.
Grab the PA with a large pair of tweezers
and remove it from the circuit board. Let the
circuit board cool for approximately two
minutes. Then remove the circuit board
from the circuit board holder.
(2) To replace the RF PA; if necessary, add
solder to the PA ground plane on the print-
ed circuit board. Then clean each PA lead
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solder pad on the circuit board to ensure
alignment of the new RF PA. Prepare the
sight by using solder wick and a soldering
iron to remove all solder from the solder
pads. Clean the solder pads with alcohol
and a small brush. Dry and inspect. Ensure
that all solder is removed.
Once the preparation is complete, place the
circuit board back in the circuit board hold-
er. Add solder paste flux to the ground
plane and to the leads' solder pads. Once
the flux is applied, place the new RF PA on
the circuit board, making certain that the PA
heatsink sits flush on the board. Position
the heat-focus head over the RF PA and
lower it to approximately 1/8"-1/4" (0.3cm-
0.6cm)) above the PA cover. Turn on the
heater and begin the reflow cycle. Heating
time should not be less than two minutes.
Once the RF PA reflows, raise the heat-
focus head and wait approximately two
minute for the part to cool. Remove the cir-
cuit board and inspect the solder joint
between the slab and the ground plane. No
cleaning should be necessary. Use the sol-
dering iron and add solder to each of the
RF PA leads and associated pads. Inspect
the lead/pad bond for opens and solder
shorts.