Service Manual Part 5
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Unsolder the leads of the transistor using solder wick or a solder sucker.
Remove the appropriate screws and carefully lift off the transistor.
Mount the new transistor using a silicon insulating gasket on the underside. Do
not use any other insulators (mica, etc) as they are unlikely to fit under Q1 and/or
would require thermal compound.
Refit the two screws for Q1 from the copper side of the PCB. Isolate each of these
two mounting screws from touching the heatsink with a 3mm length of silicone
rubber sleeving. Use spring washers under the two nuts.
Carefully position the PCB onto the heatsink before tightening the two screws/
nuts.
Ensure that Q3 sits firmly against the walls in its slot on the heatsink.
Resolder the leads of the transistor.
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Reassembly is carried out in the reverse order to disassembly.