8525B/8528 Technical Service Manual Maintenance 6-11
Publication No: 15-02036 Issue 6
6.3.4 PA and Filter Assembly
Note: The PA output transistors can be replaced without removing the
board from the heat sink. Refer to para 6.3.5.
The PA and Filter PCB (08-03021) can be removed as follows:
1. Disconnect:
• Ribbon cable(s) connecting rear panel connector(s) to the
Motherboard.
• Cable loom connecting the Option PS connector (if fitted) to the
Motherboard. (This connection is made by two 4-way connectors.
Note their positions to avoid cross-overs when reconnecting.
• The ribbon cable connecting the PA and Filter PCB to the
Motherboard. (This can be disconnected at both ends and
removed.)
• The 4-way Molex connector connecting two coaxial cables to the
PA and Filter PCB.
2. Release the two screws at each side of the PA and Filter PCB which
secure the board and the heat sink to the chassis side rails.
3. Release the two screws at the rear edge of the Motherboard which
secure it to the heat sink assembly. Note that these two screws are
shorter than the other screws securing the board.
4. Slide the heat sink assembly complete with rear panel and PA and Filter
PCB away from the chassis.
5. Release the four screws securing the PA transistors to the heat sink.
Note that at least one of these screws may be concealed by a capacitor,
one end of which may have to be unsoldered to gain access to the
screw.
6. Release the screw securing the clamp on the two driver transistors. Note
that this screw is longer than the other screws used to secure the board.
7. Release a further two screws which secure the board to the heat sink.
8. Release the earth screw and the three screws that secure the rear panel
to the heatsink.
9. Lift the board clear of the heat sink.
10. If work on the PA and Filter PCB is extensive, the dc power input lead
may be unsoldered so that the rear panel can be taken away from the
board.
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