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Kenwood KA-801(Trio KA-8700) Schematics

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by diepbtt, Apr 29, 2013.

  1. diepbtt

    diepbtt Active Member

    Messages:
    154
    I have a Trio KA-8700 japanese version of kenwood KA-801 in Europe /America.
    Curretnly i am trying to replace all electrolyte caps in all boards(Power amp except 4 10.000uF/63V i can not find, pre amp and tone control ).

    After replacing & re-assembly i powered it up in order to adjust dc offset, bias current etc.

    The amp relay clicks after 5-6 seconds but i see smokes from the transistor D313V/B507V (regulation of the pre-amp board) the heatsink is very hot so i turn off the amp and look carefully all caps in amp for correct value & direction, any short wires etc....

    Powered again and smoke comes again. So i must shut off it immediately and now look for the reasons.

    I want to look at schematics/service of this amp but the service manual download from Hifiengine, Audiokarma... seem to be not fully or has very bad quality - unable to read for my repairing purposes.

    Has someone a schematics from this amp kenwood KA-801 i would like to thank in advance.

    Further i want to know also how can i substitute these D-313V-AL/B507V-Al if they are burnt?

    PS:
    By measuring: R77/R78: 47ohm,
    R79/801,3K,
    R81/82: 1,2K
    all is as stated in the service manual

    The power supply to the pre amp i get B +/_ appr. 58 V. is it normal or?

    My knowledges in electronics is limited please help me for easy understanding why these transistors get burning if anyone can and what i must check etc.-
    thank you!
     

    Attached Files:

    Last edited: Apr 29, 2013

     

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  2. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Here are some images for the schematics (can only post one at a time with an iPad).

    Edit: It looks like the AudioKarma forums compresses the images after uploading, so these are fuzzy. If there's a particular section you're interested in let me know and I'll zoom in more closely.
     

    Attached Files:

    Last edited: Apr 29, 2013
  3. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Another.
     

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  4. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    And another.
     

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  5. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Last one.
     

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  6. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    When you say you see smoke from D313V/B507V, are you talking about Q37-40? Which one(s) in particular?
     

     

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  7. diepbtt

    diepbtt Active Member

    Messages:
    154
    It is great from you!
    I would like to thank you very much for your helping.
    Could you enlarge the sections for preamp & tone control?
    thank in advance!
     
    Last edited: Apr 29, 2013
  8. diepbtt

    diepbtt Active Member

    Messages:
    154
    I believe smokes get from the transistor Q39(2SD313V) but i am not sure whether smokes get also from Q40 (2SB507V) or not because when i first time see smokes i shut it off very quickly- I never experience it though i have re-cap some other amps like Sansui AU-D607(AU-519 in Europe/America), kenwood C1/M1 without any issues.

    I now fear to attempt powering up and seek the reason further for this transistor blowing isue!
    PS:
    This amp works perfectly before i try to recap. I intend to pro-long its life so is the purpose of my re-cap project after some successes re-capping Kenwood C1/M1 and Sansui AU-D607
     
    Last edited: Apr 29, 2013
  9. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    If it worked before you recapped then a good place to start is with what you did :)

    - Look carefully for caps you may have installed backwards. Verify with what's written on the board and in the service manual where possible.

    - Look for any inadvertent solder bridges (connections between components which aren't intended) you may have created when recapping.

    Edit: Since I have to do lots of seperate posts to put up images, I'll wait to post the images you wanted until you have a chance to check out the above.
     
  10. diepbtt

    diepbtt Active Member

    Messages:
    154


    In the power amp board i suspect i have placed wrong direction of C33 (100uF/16V) since i have not found + pole marked correctly on the board.

    Could you enlarge the power amp schematic section where the c33 locates?
    Thanks!

    I will check again all caps directions & possible sodering bridges maybe appear.
     
  11. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    That part of the schematic is already a bit fuzzy and uploading it might make it unreadable! In case it is, I can say that the + of C33 is connected to both R44 and R45 (the - is only connected to R45). I'm sure you can figure it out.

    As far as the smoking, are you sure it was a transistor and not a resistor (or something else)?
     

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  12. diepbtt

    diepbtt Active Member

    Messages:
    154


    Thank you for your help.
    I can read it and have checked this C33 direction again .
    I have placed it correctly + of C33 to both R44 & R45, - of C33 only to R45 as you suggested. So no mistake here.


    About smokes getting i think it comes from the transisitors because before i have seen the smokes getting i noticed firstly that the heat sinks of both transistors were very hot when i touched it while i wait appr. 3-5 minutes for stablity for adjustment.

    Today i check it again and find 2 issues:
    1- Wirings from pre amp board to tone control board (for power supply this tone control board) get loose and may cause short circuits

    2- on the tone control board the are two capacitors C57/58 with value 100uF/50V but in the service manual there are not stated about it.

    Could you help me further snapshotting the schematic section of these C57/57 on tone control board ?



    Today i have re-soldered the power supply wirings(from pre amp board) to tone control board after i found some broken tiny wires at the tone control board that may cause short circuit as well as checked all E- Caps for right direction.

    After doing it carefully i try to power up the amp:
    1. The relay click
    2. after 1-2 minutes i do not see smokes getting from any component of the pre amp regulator
    3. Touch the heat sinks of the 2 transistors D313V/B507V i find it is warm, but not too hot to hold it some seconds
    4. trying to adjust pre amp offset voltage adjustment:
    4a. at VR2 i can adjust it to 0V (0.03V)
    4b. at VR1 i can not adjust it to 0V, the smallest value i can get : 6,2V or much more about 20V.

    I now look for defect component in the pre amp but do not understand while i can adjust VR2 to 0V, but not at VR1? Why is the DC voltage too high in this channel?


    Thank for reading
     
    Last edited: May 1, 2013
  13. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Are you sure you're talking about C57/58? I've attached the parts list which might help.

    Figuring out why your dc offset is so high is probably beyond my ability! Hopefully EchoWars will chime in here...

    My only thought is that if the transistors were smoking perhaps they have been damaged. I bet replacements would be cheap enough that replacing them might be a good idea anyway. Maybe it might help with your dc offset?

    My KA-7100 had a very high dc offset on one channel. Two diodes in the power supply section had failed, but I replaced two transistors there as well.
     

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  14. diepbtt

    diepbtt Active Member

    Messages:
    154
    Thank you for upload the part lists of the tone control & pre amp sections.

    I have checked it again and i am sure there are 2 E-caps C57/C58 with the value 100uF 50V in the japanese version Trio KA-8700( These two E-caps stand near the yellow bush wires-total right of the picture), but Kenwood KA-801 does not have it. Therefore Kenwood does not list it in the tone control assembly.


    I think also the Transistor D313V/B507V are burnt as smokes were getting from there.

    Currently i seek replacement Tip31B/Tip 32B or NTE152/153.

    I want also replace 2SA954 and 2SC2003 but do not know, which ones are competable.
     

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  15. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Looking at the service manual, here are transistors listed along with 2SA954 and 2SC2003 - 2SC733A, 2SA1023, 2SC945 and 2SC2378.

    On another thread I read that KSA992 could be a replacement, as well as 2SA1815, 2SA970, 2SA945. But keep in mind I'm no expert on substitutions. I didn't look up anything on PNP/NPN, pin layout or whatever specs you may need to know.

    You may want to start another thread in another forum (vintage solid state?) asking about transistor substitutions. There are some knowledgable people here that might not check this Kenwood forum.
     
  16. diepbtt

    diepbtt Active Member

    Messages:
    154

    Thank you for your suggestions.
    Today i found a pair of D313V/B507 from my junk deck teac V-1RX . I will replace the old ones and see whether it gets well again or not.

    If not i may bring to a service shop and let them try to repair it.

    For a bad case i plan to canibalise it for parts for my future Trio amp i can buy:
    KA-7300D(KA-8100) or other KA-8700 or
    KA-9900(KA-907) or
    Pre -power amp set L 07C/L-05M.


    Trio -Kenwood amps, CD player or cassette deck do makes good sound but their mechanical contruction/board layout are very bad for service work.


    Thank you again!
     

     

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  17. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    Keep us updated!
     
  18. diepbtt

    diepbtt Active Member

    Messages:
    154


    Today i tried to replaces the old transistor D313V/B507V in the pre amp regulator with the good ones D313V/B507. But the condition is unchanged:
    At VR2 i can adjust to 0V
    At VR1 i can get the smallest value appr. 6,3V, just as before

    So i gess maybe a transistor or more are shot.
     
  19. rjsilva

    rjsilva Active Member

    Messages:
    444
    Location:
    PA
    I suggest you take measurements throughout the power supply section (as per the schematics) and post the measurements here. Particularly in the DRIVER and BIAS sections.
     
  20. diepbtt

    diepbtt Active Member

    Messages:
    154
    Thanks for your suggestion!
    I would like doing it but i am just beginning to learn how to meassure , check... E- components mit DMM. So is it not easy for me.

    Reading & understanding the schematics is other difficult task!

    I can measure the output voltages for the tone control at pins

    1-2(GND) : 0 V
    3-2(GND) : 0 V


    i have checked all transistors (out of the circuit) in the pre amp regulator it seem all are good but it is very strange for me that i get Pre amp DC offset more than 5-6 V as smallest value at test points 7-8. Further adjustment at VR1 not possible.
     
    Last edited: May 5, 2013

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