Kenwood KR 7600 Protection Relay Not Clicking

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by WillRobinson, May 10, 2018.

  1. WillRobinson

    WillRobinson New Member

    Messages:
    8
    Hi there, I have aquired a Kenwood KR 7600 from a local yard sale. Was told it was untested, but it's a great looking amp and for $30 I figured it was worth a gamble. Brought it home and of course, it powers on and all lights turn on but the protection relay wont click.

    I measured DC Offset and it climbs from 0 to 200mv and drops back to 0 and repeats. On both the left and right channels.

    Does anyone know what can cause this, or have tips in what to look for? Any insight would be greatly appreciated! I would love to hear this baby make sound.
     

     

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  2. rickl

    rickl Member

    Messages:
    70
    Location:
    Twin Cities
    I'd suggest downloading the service manual and look at power supply voltages. You might also want to search this forum for other KR-7600 posts. A few gems might be found.

    http://akdatabase.org/AKview/displayimage.php?pos=-604

    here are a few other KR 7600 posts.

    http://audiokarma.org/forums/index.php?threads/kenwood-kr-7600-help.657443/#post-8755843

    My guess, the receiver can be fixed. I don't have one but have read a lot on this forum to know about most of them.

    Since this is your first post, let me be the first to welcome you. Update your profile with your location. Maybe someone close can give you a hand.
     
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  3. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,043
    Location:
    Vancouver, WA
    Fairly easy to diagnose on these since you can disconnect the power amps.

    With receiver unplugged from power, remove the bottom cover and unplug both power amp channels.- the white plug connectors. Gently rock side to side while pulling - no tricks or hidden lock tabs to worry about. Plug back into the wall and power it up. If the relay clicks the problem is in one or both power amp sections. Power off and plug them in one at a time and you can figure out if it's the left or right channel.

    P1010677.JPG

    If it won't come out of protection with both amp sections unplugged the problem is likely in the power supply and the regulated voltages. Remove the top cover - power supply "A" is at the front right - board X00-1770-10. Check the following pins for DC voltages


    Pin #1 52V
    Pin #2 23V
    Pin #5 -23V
    Pin #6 -52V

    Qk1 is a usual suspect here

    P1010679.JPG
     
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  4. WillRobinson

    WillRobinson New Member

    Messages:
    8
    Thanks rickl, and gort69 for the detailed beakdown! I will perform your tests this weekend and return with the results.
     
  5. WillRobinson

    WillRobinson New Member

    Messages:
    8
    Alright here's how it went. I pulled both amp connectors, relay still not clicking. Reconnect and check voltages on Power Supply "A" board:

    Pin 1: 51.2V
    Pin 2: 1.5V
    Pin 3: 23V
    Pin 4: 51.6

    Removed Qk1 and tested it with DMM, Bingo! It tests bad. Right on the money gort! Ordering replacements tonight, I'm
    going to replace all the trannys on that board while I have it apart.

    Thanks again!
     
  6. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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  7. WillRobinson

    WillRobinson New Member

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    I'll definitely do that, appreciate the links!
     
  8. hopjohn

    hopjohn Kenwood Krazy Subscriber

    Messages:
    1,006
    Location:
    Dallas, TX
    That PS in the 7600 is a mess. The brigde rectifier is a failure point and Qk1 gets cooked by the neighboring dropping resistors. I gave mine some serious attention.
     
  9. WillRobinson

    WillRobinson New Member

    Messages:
    8
    Ok I replaced Qk1, Qk2 and Dk1,3, the other trannys are on back order. I plug it in flipped the switch, waited about 2 seconds and CLICK! She lives! Hooked up some JBL bookshelf speakers and it sounds pretty good. I was testing it out on FM and I noticed Qk1 getting pretty toasty, temp gun read 140C after 15 minutes normal volume. That can't be normal, can it? Mouser says the maximum operating temp on that transitor is 150C, seems dangerously close.
     
  10. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    504
    Location:
    San Diego, CA
  11. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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  12. WillRobinson

    WillRobinson New Member

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    Hmm, thats a great idea. I already ordered a bigger heatsink but I may just try this now. Thanks!
     
  13. EastPoint

    EastPoint Factory Code No. 4200 Subscriber

    Messages:
    4,483
    Location:
    Milwaukee, WI
    Hey folks. I actually have a 7600 with the exact same problem, and the voltages are about the same as well, so I'm going to get those diodes and transistor and go from there. Thanks for the thread, it makes this pretty easy.
     

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