Cut the tabs off the bottom of the new PTT switch to allow the switch to lay flush on the board.I used a TH-75 when they came out in 90/1991 and just picked up another one from Qrz swapshop in mint shape.Remove the screw from the PTT switch assembly and then remove the rubber PTT cover from the board.īe careful not to lose the black plastic plate that fits inside the rubber cover.Size, cut, and bend the leads of the 470 pF ceramic capacitor and then install the component between pin 59 of the microprocessor and the ground side of the 33 Kohm chip resistor.Remove the protective coating from the foil between pin 58 of the microprocessor and chip resistor R8.Replace C2 with a 33 Kohm chip resistor.Locate chip capacitor C2 on the Control board.Lay the Control board on a soft cloth to avoid scratching the LCD.Carefully lift the Control board, PTT switch assembly, speaker, and mic element from the front panel.Remove the 3 screws from the speaker mount.Remove the 4 screws from the Control board inside the front panel.To open the connectors push the tabs towards the flex cables and gently lift up. Lift the front panel from the body of the transceiver and disconnect the two flex cables.Remove the three case screws and two battery plate screws.Required parts: 33 Kohm chip resistor RK73GB1J333J 470 pF ceramic capacitor CK45B1H471K PTT tactile switch S40-1415-05 The following modification will re-configure the PTT input to the microprocessor to correct these conditions. Other users have reported symptoms such as key board lock up after transmitting. 978 (8-8-1990) Some TH-75A owners have reported that the transceiver intermittently loses its memory channel information after transmitting. TH-75A Intermittent memory loss Author: Kenwood Communication, inc. View and Download Kenwood TH-75A instruction manual online. WITH MANUAL TRANSMISSION Includes swivel. Kenwood TH-75E (TH 75E TH75E) service manual and specs. Time to perform this modification is 1 hour or less. Required part: 22V Zener diode (UZP-22B) This is an optional change that is not covered under warranty. Note: This modification has already been performed on models stating with serial number 007xxxx. The Service Manual disassembly instructions will be required to perform this modification. The Zener should be solder between the SBR side of L218 and the shielding case of L221 on the component side of the RF board (X53-3370-11) (A/3). To protect the transceiver, a Zener diode will be used to clamp the SBR line. The supply current opens L218 and the foil trace at this coil. When the transceiver is in the automatic battery saver mode, the noise pulses overcharge C348 on the RF board causing it to short. 957 (9-1-1990) When the TH-75A is connected to a vehicle battery, ignition or alternator noise can be induced on the DC line.
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