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1990-10-14
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SB-954
TA7201P Substitution Parts Kit 07/20/89
The Toshiba TA7201P audio amplifier (Q3) used in the TS-820(S) and
R-820 is no longer available. The part has been replaced with a
kit (Part # W05-0257-00). This service bulletin will provide the
correct installation procedures for replacing a defective TA7201P
with the new kit.
1. Disconnect the power cord and antenna from the transceiver.
2. Remove the covers from the transceiver and disconnect the
speaker wire.
3. Remove the AF AVR board from the bottom of the transceiver
(4 screws and 3 connectors).
4. Remove the two nuts that secure the heat sink to the audio
amplifier (Q3) and then remove the heat sink. Figure 1.
5. Desolder and remove Q3, C21, C22, C26, C33, R40, R42, and R47
from the AF AVR board. C33 and R47 are mounted on the foil
side of the board, but may not be installed on some models.
Figure 1 and 2.
6. Using the parts from the kit, install a 22 uF capacitor in the
C21 position, a 0.068 uF capacitor (labeled 683K) in the C22
position, a 3.9 ohm resistor in the R40 poisition, and a 470
ohm resistor int he R42 position. Figure 1
7. Solder a 0.1 uF capacitor (labeled 104K) in parallel with C30.
Mount the part on the foils side of the AF AVR board. Figure 1
8. Remove the two nuts from the heat sink mounting srews. Figure 3.
9. Replace the mounting screws with the ones in the kit. If the
original screws have been soldered to the board, remove the
excess solder and while the screws are still hot, turn the
board upside down to allow the screws to fall onto the working
surface. Figure 3.
10. Secure the new mounting screws with the two nuts that were
removed in step 8. Figure 3
11. Install the heat sink and secure it with the two hexagon
bosses from the kit. Figure 3
12. Insert the wires from the new audio amplifier circuit board as
shown in the diagram. Make sure the pins are firmly seated
and then solder them into place. Figure 4
13. Apply a thin layer of silicon grease to the back of the audio
chip.
14. Insert the circuit board into the heat sink and secure it with
the two nuts that were removed in step 4. Avoid pinching the
wires between the board and the bosses as well as the board
and the heat sink.
15. Attach the heat sink spring from the kit over the chip. Figure 5
16. Assemble the transceiver by reversing steps 1-3.
Note: Due to the differences in characteristics between the TA7201P
and the new audio chip, the noise level will be increased. The increase
in noise will effect the position of the AF gain control. Should it be
found that the audio is too low, the value of resistor R4 on the AF AVR
board can be reduced from 220 ohms to 82 ohms. The resistor removed
from the R40 position can be used in this situation.
(c) 103189TKC
(This bulletin is shipped with the W05-0257-00 parts kit. If you would
like a copy of it just leave a note to the sysop with your name and
mailing address.)