Modifications for the Kenwood TR-7850

TR-7850 RF LED Meter


The RF LEd meter may show reduced output after continuous transmission, while output actually remains constant. Changing components on the final unit will correct this problem. This change applies to units before serial number 201XXXX.

  1. Remove the top cover (four screws), and unplug the speaker.
  2. Remove the bottom cover (four screws).
  3. Remove four scress holding the heatsink and swing the sink down.
  4. Without changing coil spacing, desolder L6 which connects from the ANT pad aon the final unit to the PL-259, at the final unit.
  5. Remove five screws holding the final unit pcb X45-1180-10, one screw holding Q6 2SD880, and two screws holding the final hybrid module Q1, M57726.
  6. Change the following parts:

    C15 1pf to 2pf (CC45CH1H020C)
    D3 1N60 to 1S1587 (V11-0370-05)
    R8 820 ohm to 1.2K (RD14CD2E122J)
  7. Insure adequate thermal compound on Q1 and Q6, and that the mica washer is correctly positioned under Q6. Reverse steps 5 and 4 to partially assemble.
  8. Cable-up power and a dummy load. Readjust VR1 on the final unit at 147.000 MHz, high power setting for 5 LED's ON. Switch to low power and verify 3 LEDs ON.
  9. Remove power from the unit and complete reassebly by reversing steps 3, 2, and 1.

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