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Bias Setting on KR-9340

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Trodder, Aug 11, 2018.

  1. Trodder

    Trodder New Member

    Messages:
    39
    Okay Kenwood gurus, I need your help! I just don’t understand where to put my leads based on the instructions provided. What am I missing? If I am measuring current don’t I need to unplug something and measure the two connections points that were unplugged?

    I just bought this for $150 and was told everything works... well... not quite. I get protection coming on every so often and I turn it down and it comes back usually after a few seconds. For some reason I cannot have A and B channels on at the same time? Drops all dc offset to flat 0. It looks like it needs some caps replaced (naturally) and I intend to start down that path for the power and amp sections very soon. However I want to see if I can solve the protection issue first? First thought was bias. It’s weird because I can have the volume up pretty good and hold steady with no issues for 20-30 minutes. Sometimes low power will trigger as soon as I turn it up a little. Anything else I should look at specially or should I get my money back and run? The guy said he would give me my money back but it is a nice unit and it sounds great! Hearing this unit I realized that on my SX-650 the lows lack, the mids are absent, and highs are a little too bright. I love it I am just don’t want to go too far down a rabbit hole since quads are not the easiest to service and not the cheapest either. I am nervous to look up the cost of the main caps since they are monsters which of course gives me that smooth bass sound

    Included a couple noodz and shots of the SM in hopes it makes it easier to dumb it down for me! Thanks in advance!

    299FF7F6-505F-4EEF-A1B2-B73A6E4D6D34.jpeg 4C156C73-3497-45D8-BD63-3351B6037BAB.jpeg 5E1C3082-D1F6-4D91-89DD-9689A360CC24.jpeg EF95E53D-0117-4942-9793-226E4185A60C.jpeg 5E17E49D-AFA3-415B-9BBF-A4FC439696E4.jpeg
     

     

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  2. Trodder

    Trodder New Member

    Messages:
    39
    In digging further and thinking about this more.... “think” I am a little closer to figuring this out, but still unsure. First the power transistors are Q13-17 correct? Assuming the board is labeled properly and I understand the schematic, I think the emitter side of the power transistor goes to R45 and I can connect the positive lead of my meter to that leg of the resisitor? Then for the negative power supply I can connect my negative meter lead to the leg of R49 that I have circled as that appears to connect directly to B-? Can anyone confirm I am on the right path? Then the same for Q14 connecting to positive lead of R46 and negative lead for R50 where I marked and so on for the other power transistors?
    A1CAC066-C3E8-4220-8F36-F40B1A0D0D1E.jpeg
    C2D94C36-030D-4121-96D5-CDB7EE262CA6.jpeg
     
    Last edited: Aug 12, 2018
  3. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,560
    Location:
    uk.. the middle bit
    what ohm speakers are you using ?
     
  4. Trodder

    Trodder New Member

    Messages:
    39
    They are 8ohm speakers. One of them measurs 7.5ohms at the terminals and the other measures at about 7.2ohms at the terminals.
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,560
    Location:
    uk.. the middle bit
    should accept 4 to 16 ohms . so maybe the over current setting in the protect circuit needs checking after checking dc offsets . and idle bias .
     
  6. Trodder

    Trodder New Member

    Messages:
    39
    yeah I am hoping someone can tell me how to check the bias. I am still not understanding the manual on this.
     

     

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  7. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,560
    Location:
    uk.. the middle bit
    monitor dc offset first at speaker terminals..
     
  8. Trodder

    Trodder New Member

    Messages:
    39
    I still need to know how to adjust to check the bias either way. Just looking for help on how to do that.
     
  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    27,560
    Location:
    uk.. the middle bit
    its right there on page 68 .. scope is best way in my opinion .
     
  10. Trodder

    Trodder New Member

    Messages:
    39
    I don’t have a scope.
     
  11. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,083
    Location:
    Dallas, TX
    The instructions suck A scope would be best. Here is what the SM should have said.
    Output transistors pairs are Qe13/Qe17, Qe14/Qe18, Qe15/Qe19, Qe16/Qe20. You need to make a current reading (NOT Voltage) for each one of the four output pairs set to 50mA so set your DMM accordingly.
    Assuming the schematic is correct...
    Adjust VRe1 for Qe13/17, leads on pins 8 and 5, to 50mA
    Adjust VRe2 for Qe14/18, leads on pins 8 and 14, to 50mA
    Adjust VRe3 for Qe15/19, leads on pins 28/29 and 24/25, to 50mA
    Adjust VRe4 for Qe16/20, leads on pins 28/29 and 35/36, to 50mA
    Do as the instructions suggest by resetting after a half-hour warmup.
     
    Last edited: Aug 13, 2018

     

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  12. Trodder

    Trodder New Member

    Messages:
    39
    When you say pins, do you mean the numbers that are at the bottom of the card where it slides into the base? I am a little leery since I tried to use the little mini grabbers on my meter leads and put them at the locations I though and I have alreaeyd smoked the trimmer and one of the other resistors.... hopefully not much more but I am going to replace the caps and transistors anyway just to be safe.
     
  13. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,083
    Location:
    Dallas, TX
    Yes, the corresponding contacts on the PC board.
    if you can't find anything to to clip onto find a way to insulate anything you may slip and touch around your measure points. Masking tape.....whatever you've got.
     
  14. Trodder

    Trodder New Member

    Messages:
    39
    Fantastic! Than you so much! I am going to swap parts before I go any further at this point since there is no telling what damage I caused already, but I hope to get that done in the next week or two. Just trying to shore up my parts list. The trimmer pot is the piece i have having the most issues with. I am wondering if I can make one that is 9mm wide work since the originals are 11mm wide. Naturally that changes where the pins line up a bit.
     

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