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Kenwood KR-6600 left side speaker "popping" sound

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by vmedia, Dec 2, 2018.

  1. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    Hello.
    I have not been able to find a solution to my problem in other threads, so I thought I would give my own a try.
    I have a Kr-6600 that sounds fantastic (after Deox-ing pots and switches) but I'm experiencing a rather loud "pop" in the left speaker when switching between aux and phono 2 and Fm and phono 1. I have cleaned the sliding switches on the pre-amp board twice with Deoxit and Fader lube as well as all other pots and switches. I have set the bias on both channels (40mv) and reflowed any solder joints that looked even the least suspicious (this includes checking and re-soldering any obvious grounding points on the pre-amp board.
    I have also re-capped the pre-amp board with no real noticeable improvement of this issue. I have tried two different turntables and the pop is the same for both.
    One curious note, I did notice that, when I accidentaly plugged my CD player into the Phono inputs (on pause, thankfully!) the pop when switching sources was no longer there.
    Not sure where to look next, pre-amp transistors or power supply board?
    Any help would be most appreciated.
     

     

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  2. Ray Gianelli

    Ray Gianelli AK Subscriber Subscriber

    Messages:
    1,112
    Location:
    Lake Worth, FL
    I'd check for DC leakage from the left phono stage. ICd1 is cap coupled, but there may be some leakage around there causing the pop. Check all voltages from schematic around the IC.
     
  3. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    EDIT: Schematic in AK database is much clearer than the one I found on HiFi.
    Will check voltages and report back ASAP.


    Thanks for the response.
    I clearly see two voltages on the schematic - 2.5mv at the negative side of Cd1 and 150mv positive side of Cd11 - I'm guessing that there are more shown in the "bubble's" around Icd1, but not readable (see attached)
    Are there more? I ask, because this is a bit of a job pulling apart and checking under power while apart.
    Also, I'm not familiar with the numbering system on this schematic. What's the extra "d" for in each component's part designation?
     

    Attached Files:

    Last edited: Dec 2, 2018
  4. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    OK - Voltages are as follow (Source set to aux, volume at 0, measured with selector on Aux as well as Phono 1 with no change)

    1) 17.43vdc
    2) 5.8mvdc
    3) 0
    4) -18.14vdc
    5) -16.8vdc
    6) 4-5.4mvdc (fluctuates)
    7) 18.05vdc

    I also touched up more solder joints anywhere near ICd1 with no change when tested.
     
  5. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,118
    Location:
    Vancouver, WA
    From an original schematic

    Pin 1 16.8V
    Pin 5 -15.2V
    The others (2,3 & 6) 0V

    Screen Shot 2018-12-02 at 8.44.13 AM.png

    The selector knob operates two switches - the slider on the pre-amp board and a rotary switch immediately behind the faceplate frame - make sure both are cleaned. Also - the sound injection switch/pot can cause all sorts of oddball noise - make sure it is well cleaned also.

    The "d" is the designation for the components installed on the pre-amp board. The power amp board is "e", the tuner is "g", etc. You'll get the idea looking at the parts list.
     
    Last edited: Dec 2, 2018
  6. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    I think you may have missed my previous comment that I found the schematic here on AK that had the voltages clearly marked, but thanks for adding to the drawing (helped to confirm that I read them correctly)
    Any thoughts on the voltages I posted?
    Also, I've cleaned both sides of the selector switch as well as the sound injection (and did it just now again) thump is still there as strong as ever. Possibly a cold solder joint on the selector rotary switch? Not sure which are the phono connections...
    Thanks for continuing to help.
     

     

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  7. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    Thoughts anyone?
    Wondering a if need to start testing transistors and resistors in the phono stage?

    As a reminder, when I hook up my cd player to the phono inputs (not sending signal) the thump goes away when switching in and out of phono. When a turntable is hooked up (tried two different units properly grounded) the thump is still there.
     
  8. vmedia

    vmedia AK Subscriber Subscriber

    Messages:
    89
    UPDATE:
    Success! Turns out the issue was in fact a bad solder connection between ceramic cap Cd23 and the chassis ground. The pad had lifted but was hidden by a glob of solder (presumably factory) and I missed this until I de-soldered the cap wire while double checking all grounds. Just for the record, cleaning the slider switches did clean up an intermittent loss of sound on the left side, but I have a sneaky suspicion it was actually this ground issue causing the signal loss. Thanks to Ray and gort69 for helping troubleshoot. This unit sounds great and was worth the extra time to make right.
    All the best.
     

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