Tait T830 Series, Руководство по обслуживанию

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Copyright TEL 31/01/96
4 To Replace PA Transistors
Caution:
As the location of certain components in the PA is critical to perform-
ance, it is important that any components removed or disturbed are
refitted in
exactly
the same position.
Caution:
Before attempting to remove a transistor, measure the distance
between the capacitors and transistor body to the nearest 0.5mm (meas-
urements "A" and "B" in Figure 4.1) so that the capacitors can be
replaced in
exactly
the same position. These measurements are shown
in Figure 4.1 for the 6LFL package, however the same procedure
applies for the SOE (stud) package.
Caution:
Do not solder the tabs before torquing down otherwise the device may
be broken.
Desolder the tabs by heating with a soldering iron and lifting away from the PCB
with a thin stainless steel spike, or screwdriver. Unscrew the transistor stud nut
and remove the device.
Trim the tabs of the replacement device to make them similar to the faulty device,
and tin the underside lightly. Smear the face of the device with heatsink com-
pound and tighten it securely (torque setting 8lb-in./0.9Nm) to the heatsink. Then
solder the tabs.
Replace each capacitor in exactly the same position as measured previously.
Figure 4.1 Typical Transistor/Capacitor Spacing (Not To Scale)
measurement A measurement B
base collector