C5.20
T856/857 Fault Finding
M850-00
31/09/98 Copyright TEL
Q410 Only: Unscrew the transistor stud nut and remove the device.
Remove any excess solder from the PCB pads with solder wick.
Trim the tabs of the replacement transistor so that the device sits neatly on the
PCB pads provided.
Lightly tin the underside of the transistor tabs.
Apply a small amount of heatsink compound (Dow-Corning 340 or equivalent) to
the transistor mounting surface. Sufficient compound should be used to ensure
an even film over the entire mounting surface.
Place the transistor on the PCB in the correct orientation and ensure the tabs are
flush to the surface.
Q410 Only: Lightly solder one tab to the PCB, then torque down the retain-
ing nut to the correct torque (0.7Nm/6lb-in.).
Caution:
Do not solder all the tabs before torquing down otherwise the device
may be broken.
Q420 Only: Refit the solder tags.
Solder all transistor tabs to the PCB.
Replace each component in exactly the same position as noted previously.
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