Maintenance
HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual 5-15
Replacement of PA transistors
The PA output transistors V23 and V24 should only be replaced as matched pairs.
The gain groupings of the SRFH1008 (selected MRF455) transistors are identified
by a letter code and should be the same.
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.
q Unsolder and remove the capacitors C107 and C108 located between the
collectors of the transistors.
q Unsolder and lift the driver transformer T3 secondary winding from the
transistor bases.
q Remove the screw located between the heatsink fins that secures the output
transformer to the heatsink.
q Unsolder and lift the output transformer T4 from the transistor collectors.
q Remove the flange fixing screws.
q Use a de-soldering 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.
q Clean away excess solder from transistor pads on the PCB.
q Clean the transistor mating surface on the heatsink with a cloth or tissue.
q Coat the transistor flange with a thin film of thermal compound (e.g. Jermyn
Thermaflow). Note that you must not use too much thermal compound.
Check the orientation and fit the new transistors.
q Refit the four flange mounting screws complete with the three solder lugs.
Tighten the screws evenly.
q Carefully solder the transistor connections. This should be carried out
quickly using a very hot soldering iron.
q Replace the screw that secures the output transformer to the heatsink.
q Solder the output transformer primary to the collectors and solder in
capacitors C107 and C108.
q Re-adjust the bias current (see page 7-23, PA adjustments).
To Next Page
Loading...
Need help?
General
