Kenwood KR 7600 no safety relay click

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by srinath, Jun 26, 2017.

  1. srinath

    srinath Super Member

    Messages:
    2,449
    It was sitting for atleast 2yrs before I got it.
    Its doesn't click the relay. More interestingly, I pulled all the connections to the power amp.
    Still no click.
    What is that soldered one on top that seems to power up the tuner dial but seems to have a white and red wire going to the speaker terminals ??? I didn't desolder that.

    Thanks.
    Srinath.
     
  2. sregor

    sregor AK Subscriber Subscriber

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    Unit requires the voltage regulators to be correct voltage or no relay also. Usually positive regulator pass transistor. (2sc1419 but has probably been replaced before....)
     
  3. gort69

    gort69 AK Subscriber Subscriber

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    Location:
    Vancouver, WA
    - Check for continuity on the power switch

    - Check the fuse that is on the left end of the lamp panel board by the dial cord pulley - if it's blown, no click (no dial lamps either)

    - Check the filter caps for +/- 52V DC. 0 here means a likely bad rectifier

    Regarding the regulators (Qk1,5), check pins 2 & 5 on power supply A (right front) for +23VDC and -23VDC respectively. There are a couple of 24V zeners (Dk1,3)that can fail on that board as well and screw up those voltages also

    Not familiar with the red & white wires - can you post a picture?
     
    Last edited: Jun 26, 2017
  4. srinath

    srinath Super Member

    Messages:
    2,449
    Thanks. I will go looking for that.

    That fuse is intact, I looked. I have lights all around.
    I'll look for 52V, I suspect that that little thing red+white wire is a low voltage deal to make the tuner needle tip glow red. I'll voltage test it. Likely some low voltage.

    Thanks.
    Srinath.
     
  5. srinath

    srinath Super Member

    Messages:
    2,449
    Under no load I have +/- 53.3 @ the big caps.
    However I cant find Qk1,5 or Dk1,3 - right front power supply A board ? You mean when facing the amp ???
    And cant find 2sc1419 either. What board is that on ?
    I will have to find its schematic as well.
    The red+white is a little 2V DC to light up the pointer.
    Thanks so much guys.
    Srinath.
     
  6. srinath

    srinath Super Member

    Messages:
    2,449
    OK found that power supply board - exactly where you said it would be Gort69.
    I've got to find 2sc1419 too. Schematic really helps.
    Thanks.
    Srinath.
     
  7. srinath

    srinath Super Member

    Messages:
    2,449
    OK 22v @ pin 2 vs chassis ground.
    7v @ pin 5 vs chassis ground.

    Awesome - dead Qk5 and check Dk3 as well ???
    Actually Qk5 has left a little black smudge on that capacitor in front of it.
    Thanks.
    Srinath.
     
  8. gort69

    gort69 AK Subscriber Subscriber

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    874
    Location:
    Vancouver, WA
  9. gort69

    gort69 AK Subscriber Subscriber

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    You posted as I was typing - yes, I think you're on the right track. Test Q5 and Dk3.

    Qk1 is the 2sc1419
     
    Last edited: Jun 26, 2017
  10. srinath

    srinath Super Member

    Messages:
    2,449
    Qk5 I'm sure has gone to 3 legged heaven. Not sure if it took Dk3 along with it.
    I have to test it - for now I'll have to shelve it. Life calls.
    Actually other amp calls.
    Thanks.
    Srinath.
     
  11. srinath

    srinath Super Member

    Messages:
    2,449
    For tha t24V zener diode - can I sub in 1N4749A or something like that ?
    Cos I may have it.
    I probably have a 100 of both in all the dead amps I have. Time to raid the onkyo that's been kicking my butt.
    Thanks.
    Srinath.
     
  12. gort69

    gort69 AK Subscriber Subscriber

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    Location:
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    I use 1N5252B, 24V .5W. I'm not smart enough to say what else might work. 1N4749A shows to be 24V 1W
     
  13. srinath

    srinath Super Member

    Messages:
    2,449
    Oh man, you know this amp really really well.
    Thanks.
    Srinath.
     
  14. Nuel

    Nuel New Member

    Messages:
    4
    I am facing the same problem. Just picked up one with protection relay tripping when switched to FM or AM .Other sources and everything else work fine (dial lights, tone board, power amp etc). Happened to see a partially burned Power Supply "A" board. Filter cap Voltage is +/- 51.5 VDC, so that is good. Voltage at PIN 2 & 5 are +37VDC and -37DC respectively instead of +/-23V. Zener Dk1 dead along with it, it took Qk1. C4 might fail eventually, it is bulged and runs hot. I'm going to rebuild this board. Any suggestions for equivalents for Q1 and Q5?
     
  15. gort69

    gort69 AK Subscriber Subscriber

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  16. Nuel

    Nuel New Member

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    Thank you Al,
    I replaced all the components on the right side of Power Supply "A" board (except for ceramic caps).
    Qk1 is the same as you mentioned.
    Qk2 is https://ca.mouser.com/productdetail/512-mje170stu

    Voltage across PINS 2 & 5 starts at little more than +/- 23V, but it slowly increases to +23.7V and -24V respectively. However the main issue is that, that side of the board starts to heat up drastically around the same area it had it originally burnt (Qk1, R1,R2,R3,R18). My guess is the problem still persists somewhere and Qk1 is going to blow again.
    Qk5 runs cool. Relay clicks fine.

    Here are the voltages
    Qk1: E->23.7 ,B->24.3 ,C ->42.1
    Qk5: E->24 ,B-> 24.6 ,c-> 38.6

    FM works just fine, including meters and stereo light. Sound from headphones is crystal clear.
    Tried with the power amp disconnected, but still it heats up.
    Any pointers??

    Kenwood_KR_7600_PS_A_Bottom.jpg Kenwood_KR_7600_PS_A_Top.jpg
     
  17. sregor

    sregor AK Subscriber Subscriber

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    Location:
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    Every one I've ever seen runs hot. The issue is that the heat eventually causes the transistor to fail (usually open) (but the replacement is much heartier and failure resistant than the original part - so it will probably last a very log time) and can cause problems with the PC board (as you can see)
    There is power that needs to be dissipated. Three things can be done. (well, 3 that I thought of, there may be others). First would be to drop some of the collector voltage through a resistor. - I would start with a 10 ohm, and measure voltage drop (in am, fn and phono modes) to determine how much current is involved, then increase resistance to drop about 8 to 10 volts. (at highest current draw) (figure 5 to 10 watts and mount on the chassis if possible) Right now the voltage drop is about 20 volts, and produces the heat. Second option is bigger heat sink. (If you have time, peruse some of the Pioneer sx780 power supply mods and problems). The third option is to mound the transistor directly on the chassis, (actually is same as bigger heat sink, except gets the heat producing source off the board) A reminder is that the metal tab is the collector, so has voltage on it. Means you have to be careful that heat sink is either not near anything grounded, or the transistor is mounted with a mica or insulator pad and with an insulated shoulder on the mounting screw.My 2+ cents...
     
    Last edited: Dec 16, 2017
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  18. hopjohn

    hopjohn Kenwood Krazy Subscriber

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    Location:
    Dallas, TX
    I posted about this very thing a few weeks ago. Here's the relevant info from that post....

    Moving the regulators off board
    The regulators on the KR-7600 on are in close proximity to several resistors which get pretty darn hot. Qk1 is particularly vulnerable and is why it is given such a large heat-sink. Rather than try to keep those cool next to components that will always run hot, I've moved them off board underneath the PS.

    I make use of the heat-sink from the original odd-ball rectifier which I had replaced. There are three holes in the chassis rail where the PS screws down, but only 2 holes are used so adding a third hole through the PS board allows me to take advantage of that hole and mount the heat-sink. Both regulators are then isolated with mica and plastic shoulder washers. After adding some thermal compound I screw them into the existing threaded holes. I follow that up by adding some split washers, nuts, and thread lock to the back to make sure they stay in place. Using some hook-up wire I route the appropriate BCE connections to the board and tidy it up with some heat-shrink insulation.


    [​IMG]
     
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  19. Nuel

    Nuel New Member

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    You guys are of great help.Thank you very much. So I am guessing the transistor getting extremely hot is just normal. I am inclining more towards mounting the heat sink to the chassis. Will do it soon. The only thing that concerns me is that the resistors in that section also gets just as hot, toasting the PCB. Is it okay to leave them there?
     
  20. Nuel

    Nuel New Member

    Messages:
    4
    So I finally got around to moving the transistor to the chassis. There was a perfect little spot with a lot of contact surface, so screwed it right there. Now the chassis gets hot, transistor is relatively warm. Played this monster for several hours and it works like a charm. This will be fine for many years to come. Thank you everyone that helped my little project.

    IMG_3816.JPG
     

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