Tait TB8100, Service Manual

Page: 182 / 306

182 Power Amplifier Board Replacement TB8100 Service Manual
© Tait Electronics Limited September 2006
10.3 Replacing the 60W Board
Important
There is heatsink compound between the RF power tran-
sistor and the heatsink. You may need to carefully prise the
transistor away from the heatsink with a small screwdriver.
Any objects caught in the heatsink compound underneath
the transistor which prevent effective grounding and/or
heatsinking may cause the transistor to fail.
Important
If you replace the 60W board, you must recalibrate the PA
bias using the Calibration Kit. Refer to the Calibration Kit
documentation for more details.
Refer to “Power Amplifier Disassembly and Reassembly” on page 173 for
details on removing and refitting the cover, and for screw torque settings.
The circled numbers in the following instructions refer to
Figure 10.3 on
page 183 .
Removal 1. Remove the cover.
2. On a 12V 50W PA, remove the boost regulator board (as described
in
“Replacing the Boost Regulator Board in a 12V PA” on
page 193 ).
3. Remove the bridging links
b
connecting the board to the control
board.
4. Desolder the red +28VDC power feed wire
c
. On a 12V PA, also
disconnect the black earth wire.
5. Desolder the RF links
d
connecting the board to any adjacent
boards.
6. Remove the 4-40 UNC Allen screws
e
securing the RF power
transistor
f
to the heatsink.
7. Remove the M3 Torx screws securing the board to the heatsink.
8. Carefully lift the board directly upwards off the locating pins
g
and
remove it from the heatsink.
Refitting the
Original Board and
Transistor
Use the following instructions if you are fitting the original 60W board and
RF power transistor, and haven’t disturbed any of the solder joints around
the transistor.
1. Ensure the heatsink and bottom of the transistor are clean. Remove
any old heatsink compound.
2. Apply a thin layer of fresh heatsink compound to the bottom of the
transistor. Use as little as possible, while still covering the whole of
the mounting area of the transistor.
12V
28V 12V