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Kenwood KR-770 Power meters dead

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by rocknroller, Oct 17, 2018.

  1. rocknroller

    rocknroller Active Member

    Messages:
    379
    None of the left and right red LEDS light when in use, only the center green led. Per the schematic (attached) there is -9.7 on the left and right and -10.8 on the common, so those inputs look like they match the schematic values pretty close. However, I don't understand how the LED circuit actually works and shows the measured power. Can someone explain what is supposed to be happening in the circuit?
     

    Attached Files:

     

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  2. llwhtt

    llwhtt Super Member

    Messages:
    1,471
    Location:
    SoCal
    The output of each channel goes to IC3 which in turn drives Q29 and Q30. The signal on the emitters of Q29/30 then turns on each transistor on the meter PCB according to the signal level. As the transistors on the meter board turn on the appropriate LED will light. So IF all of your DC voltages appear to be correct AND with NO level LEDs lit the only common part for both channels would be IC3. I would start checking the in and outs of IC3.

    Craig
     

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