Kenwood TK-8102H Service Manual page 15

Replacing a Drive FET (Q801)
1. When replacing the Drive FET, you must also replace its
heat conductor cube, because the heat conductor cube is
removed along with the FET.
2. After removing the FET and its heat conductor cube, sol-
der a new Drive FET to the PCB. Make sure the FET is in
the proper position before soldering.
3. Attach the heat conductor cube to the FET as instructed
below.
How to Solder the Heat Conductor Cube
1. Place a piece of soldering wire (about 2.5~3.0 mm long x
0.6mm diameter) into the FET hole on the PCB ( q ).
2. Place the heat conductor cube on the PCB surface beside
the FET hole. The rounded surface of the heat conductor
cube must face upward (as shown below) ( w ).
3. Slide and drop the cube into the FET hole so that the
rounded surface of the cube is now horizontal (as shown
below) ( e ).
1
PCB
Drive FET
Q801
Fig. 1
4. Place a heated soldering iron onto the top of the cube,
using an iron tip 900M-T-3CF. Hold the soldering iron in
position for about 5 seconds (See the figure 2).
PCB
Drive FET
Fig. 2
45°
3.0mm
(0.118")
900M-T-3CF
ADJUSTMENT
3
2
4
17mm
(0.670")
5. The solder melts and binds the FET and the cube se-
curely. Then, slide the soldering iron along the PCB sur-
face to cool the soldering down ( r ). If the heat conduc-
tor cube comes off from the PCB or the soldering can be
seen on the top of the plate, the soldering has not been
successful. The soldering must bind the heat conductor
cube and FET securely (see the figure 3).
OK
Uneven
PCB PCB
Drive FET Drive FET
Fig. 3
6. After soldering the heat conductor cube to the PCB,
check the level of PCB surface. The surface of the heat
conductor cube must be free of flux and solder. It must
be flat and smooth, at the same level as the PCB surface
(as shown below).
PCB
Drive FET
Fig. 4
How to Check the Heat Conductor Cube Surface
1. Slide your index finger along the PCB surface (as shown
below) ( t ).
The surface should be flat and smooth. If you feel that
the surface is uneven because of solder or flux, grind
them using meshed copper or re-solder the cube in order
to flatten the surface.
PCB
Drive FET
Fig. 5
TK-8102H
NG
Solder
PCB
Drive FET
5
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