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Kenwood L09M Repair, Refurbish, Upgrades, Questions.

Discussion in 'Solid State' started by blfttieq, Jun 19, 2018.

  1. blfttieq

    blfttieq New Member

    Messages:
    39
    I posted here many years back when I first needed some fan repairs. EchoWars was all help with that and this amp has served as a sub amp for 7 years. The history is I purchased this amp for the cost of repairs were it was abandoned by the previous owner. I have less than 200 bucks in the amp. Recently the amp has developed a hum and some intermittent sounds that to my non expert ear sound like a component in the audio path. The sound is scratchy and airy much like a dying transistor. So I have questions and have a refurb plan, but would appreciate your feedback on this.
    1. I have disassembled the amp. the power board and heat sink are out. I have thus far resoldered the entire transistor to heatsink mounts (with Sankens out). The Sankens and insulators are cleaned and back in with fresh heatsink compound. The fan is not that old and still quiet, so just new dampers on it.
    2. I have identified some faulty components in the protection circuit. Qf15 / Rf59 /Df11 & Df12 are looking bad and I am sure this transistor is burnt up. There are several items that have questionable solder joints and of course I will resolder all suspect joints.
    3. All the electrolytics are original excepting for 1 or 2. I plan to replace every electrolytic capacitor including those GIANT 18000uf 160V cans.
    Questions:

    Mouser has ChemiCon E36D161HPN183ME92M standard type capacitors in stock. Is there anything wrong with using a Non Audio grade cap in the main caps positions? Have I chosen the right dimensions?
    I have all the caps and relays and more items in a Mouser cart right now. very reasonable I think.

    Qf15 > currently that burnt transistor is an A1837. This is also the only place in this amp that I can see a non original transistor and some previous repair.
    I plan to put NTE288 in that position and rebuild components around it.
    Could this transistor cause the intermittent audio I experienced? Df11 & 12 are W06B I plan to use 1N4003 is that good to go. I want to replace all those W06Bs on the boards.
    Is there a better part to use for Qf15? Should I replace Q14 to something related to the NTE288 part?

    What operational items should I check that may have led to the failure of Qf15? This looks like the 2nd time to repair this circuit area.I have the full service manual Thank GOD but I am still not an EE just a long time hacker, Im much better on Tube Gear. Still so much of the symmetry of this schematic is so similar to tube amp topology. Especially the diff amp configs and the splitters.


    When i put it all back together I am considering some staked in turrets to eliminate this pin wrap crap. Also want to upgrade speaker binding posts but after searching here and other places just not sure the best product within reasonable money.
    Are there any upgrades that I need to consider since the post several years back on here where the thread was the OnSemi transistors.
    How can i test these Sankens if they are so static sensitive?
    Ok thats a LOT of questions and I have a few more concerning test setup. to be continued

    Thank you if you read this far down.
     
    Last edited: Jun 19, 2018
    Ds2000 likes this.

     

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  2. ivandezande

    ivandezande Super Member

    Messages:
    1,703
    Location:
    Twin Cities
    That cap looks perfect, whatever "audio grade" means doesn't matter, that cap has high ripple current and is the right specs so it's perfect. Make sure it's not too tall.
    Woah, don't use NTE parts...MJE15033 should be fine, although someone should back me up on that.
    Sounds like you should just rebuild the board honestly. New silicon is cheap and gives peace of mind, especially since you said it looks to have had issues before.
    Original binding posts look fine to me!
    Good luck, I'm sure others will give some info as well.
     
  3. blfttieq

    blfttieq New Member

    Messages:
    39
    Some pics of this project.
     

    Attached Files:

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  4. blfttieq

    blfttieq New Member

    Messages:
    39
    Thank You for the feedback. I'm not at all opposed to your advice on all new transistors. I do have this out and with the pins & wire wrap layout I don't want to pull it out any more than I have to.
    Excellent to know of another device to use. I assume that is OnSemi, but Im about to google it or Mouser it...
     
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  5. blfttieq

    blfttieq New Member

    Messages:
    39
    the diodes that are W06B I found a datasheet so 1N4001 no good. I edited above to 1N4003
     

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  6. blfttieq

    blfttieq New Member

    Messages:
    39
    Anybody have any feedback or help on the protection circuit? Any transistor equivalents? What would you use for the 2SC1775A or the 2SA915?
     

     

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  7. ivandezande

    ivandezande Super Member

    Messages:
    1,703
    Location:
    Twin Cities
    2SA915 > KSA992
    2SC1775 > KSC1845
     
  8. ivandezande

    ivandezande Super Member

    Messages:
    1,703
    Location:
    Twin Cities
    Here's a nice sub guide.
     

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  9. blfttieq

    blfttieq New Member

    Messages:
    39
    Thank You ivandezande! I have been going about blind reading transistor specs. The KSA992 is one of the datasheets I have on the screen. i have to look again tomorrow. Seems like 1 of the parameters I had a question on. I like those MJE and MJF series also but not sure which is best. I really wish I could understand what that circuit is doing more clearly. It just seems looking at it that the current to operate those relays would be more than the 2SA915 1 watt.

    Update, since reading the datasheets for the relays, I now understand they work at a much lower current than I assumed. So with research I'm feeling better about going forward.
    Also not going to replace any transistors just to upgrade. going to focus on the area of the protection circuit, ancient diodes, and some key transistors, all the relays and all electrolytics, resistors yeah a bunch of them lol
     
    Last edited: Jun 22, 2018
    ivandezande likes this.
  10. Mark B

    Mark B Yamaha Fan Subscriber

    Messages:
    5,573
    Location:
    usa
    Nice work.

    I owned a pair of L09M's - after EchoWars refurbished them they were fantastic amplifiers! A friend has them now.
     
    Ds2000 likes this.
  11. blfttieq

    blfttieq New Member

    Messages:
    39
    Thanks Mark B
    I wish the expert that is EchoWars would chime in. Do you recall any specific mods or substitutions he made.
     

     

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  12. blfttieq

    blfttieq New Member

    Messages:
    39
    What do I need to use for LED in the meter pilot light?
     
    Last edited: Jul 4, 2018
  13. blfttieq

    blfttieq New Member

    Messages:
    39
    Made a tool for staking in some turret terminals. I'm not a fan of the soldered pins on this amp. My Mouser order arrives tomorrow. She will have all new electrolytics. In this process I've found multiple solder joints that were questionable with age fatigue etc. Not saying 20180702_103827.jpg 20180627_102346.jpg 20180701_131052.jpg those are failures but could have been in the future.
     
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  14. ghamilton

    ghamilton Super Member

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    1,480
    Location:
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  15. Mark B

    Mark B Yamaha Fan Subscriber

    Messages:
    5,573
    Location:
    usa
    Glenn replaced the output transistors with On-Semi MJ21195 and MJ21196. The stock 18,000µF 120V filter caps were replaced with 22,000µF 160V caps. The cooling fans were replaced with ebmPapst fans.
     
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  16. blfttieq

    blfttieq New Member

    Messages:
    39
    My Mouser order came and went. Everything back together except for the big caps and some grounds. I tried to.improve the wire paths and space. Deciding on the pilot lamp mod. Leaning towards a green led.

    20180704_154610.jpg 20180704_154546.jpg 20180703_203303.jpg 20180703_192909.jpg
     

     

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  17. blfttieq

    blfttieq New Member

    Messages:
    39
    What other mods or improvements can I make. I read where Glen put some type of cap across the power supply caps on an amp and also replaced all the zenner diodes.
     
  18. Mark B

    Mark B Yamaha Fan Subscriber

    Messages:
    5,573
    Location:
    usa
  19. blfttieq

    blfttieq New Member

    Messages:
    39
  20. blfttieq

    blfttieq New Member

    Messages:
    39
    The big caps get here tomorrow.
     

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