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                             K E N W O O D
   >>>   A M A T E U R   R A D I O   S E R V I C E   B U L L E T I N   <<<
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                        Kenwood Service Centers

   Kenwood Service Corporation             Kenwood Service Center, East
   2201 East Dominguez Street              829 Lynnhaven Parkway, Suite 130
   Long Beach, California 90801            Virginia Beach, Virginia 23452
   Telephone 1-310-639-5300                Telephone 1-804-340-1702

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BULLETIN # 978
MODEL: TH-75A
SUBJECT: INTERMITTENT MEMORY LOSS

Some TH-75A owners have reported that the transceiver intermittently 
loses its memory channel information after transmitting. Other users 
have reported symptoms such as key board lock up after transmitting. 
The following modification will re-configure the PTT input to the 
microprocessor to correct these conditions.

REQUIRED PARTS:

33K OHM CHIP RESISTOR	        RK73GB1J333J
470pF CERAMIC CAPACITOR	        CK45B1H471K
PTT TACTILE SWITCH		S40-1415-05

1. Disconnect the battery and antenna.

2. Remove the three case screws and two battery plate screws. Figure 1

3. Lift the front panel from the body of the transceiver and disconnect 
   the two flex cables. To open the connectors push the tabs towards the 
   flex cables and gently lift up. Figure 2

4. Remove the 4 screws from the Control board inside the front panel. Figure 3

5. Remove the 3 screws from the speaker mount. Figure 3

6. Carefully lift the Control board, PTT switch assembly, speaker, and 
   mic element from the front panel. Do not break any wires.

7. Lay the Control board on a soft cloth to avoid scratching the LCD.

8. Locate chip capacitor C2 on the Control board. Figure 4

9. Replace C2 with a 33K ohm chip resistor.

10. Remove the protective coating from the foil between pin 58 of the 
    microprocessor and chip resistor R8. Presolder the exposed foil. Figure 5

11. Size, cut, and bend the leads of the 470pF ceramic disc capacitor and 
    then install the component between pin 59 of the microprocessor and 
    the ground side of the 33K ohm chip resistor. Figure 6

12. Remove the screw from the PTT switch assembly and then remove the 
    rubber PTT cover from the board. Be careful not to lose the black 
    plastic plate that fits inside the rubber cover.

13. Remove the PTT switch from the board.

14. Cut the tabs off the bottom of the new PTT switch to allow the switch 
    to lay flush on the board. Figure 7

15. Install the PTT switch.

16. Assemble the transceiver.

Time required to perform this modification is 1 hr. or less.