Replacement Of Pa Transistors - Codan X-2 Service Manual

X-2 Technical Service Manual
2.
3.
4.
To install the PA PCB assembly to the main frame:
1.
2.
Depending on the nature of the repair it may be necessary to reset the bias
and power levels. Refer to PA adjustments in Chapter 7 for details.
5.4.6

Replacement of PA Transistors

The PA output transistors, V18
matched pairs. The gain groupings of the SRFH1008 (selected MRF455)
transistors are identified by a coloured dot or letter code. Only transistors of
the same dot colour or code should be fitted.
The PA output transistors can be replaced without removing the PA and
Filter PCB from the heatsink. It is necessary to release only the screws
securing the transistors and to unsolder connections as follows:
1.
2.
3.
4.
5.
6.
7.
Publication No: 15-02047
Carefully refit the PCB to the heatsink taking care to locate R22 and
V16 into their appropriate holes and check the mica insulator remains
in place under transistor V17.
Loosely fit all screws (ensuring the longer screw is located in the driver
heatsink), then tighten.
Reconnect the wires and solder lugs to the antenna sockets. Install the
DC input power leads. Take care not to overheat the plastic insulation.
Carefully slide the assembly from the rear of the transceiver onto the
septum panel. At the same time locate the Antenna Control connector
J401 through the cut-out in the rear panel.
Once in position, refit all screws and tighten.
Note: The 16mm long screw is fitted in the hole located between
transistor V19 and the driver heatsink securing the PCB via the
heatsink to the septum panel.
Unsolder and remove the capacitors C87
the bases of the transistors.
Unsolder and lift the driver transformer T3 secondary winding from the
transistor bases.
Cut and remove the cable tie supporting the output transformer T4 to
the PCB.
Unsolder and lift the output transformer T4 primary winding from the
transistor collectors.
Remove the flange fixing screws.
Use a desoldering tool or 'solder wick' to remove the bulk of the solder
at each connection. Remove the solder lugs from the emitters of the
transistors. Gently pull the transistor legs away from the PCB while
heating the joints.
Clean away excess solder from transistor pads on the PCB.
[E11] and V19, should only be replaced in
to C89 located between
[E10]
Maintenance 5-11