Accuphase C-200 factory discrepancies

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by nj pheonix, Aug 12, 2017.

  1. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    First i'm no guru. This was a a listening and observation that created this thread.

    I’m presenting this as a service to anyone opening up an Accuphase C-200 preamp.

    I purchased this about 6 months ago but hadn’t dug into it until about 2 months ago. It came to working though I thought it lacked something sonically. I had hoped it just had tired caps and it would sing nicer after the elytics were replaced. As a side note the power board had a couple of disintegrating resistors and I replaced them all (precautionary, they did all tend to meet spec.) After replacing the electrolytics, I still didn’t think it sounded quite right.

    Thinking perhaps a tone section issue (which admittedly is more complicated than I understand) I started checking components against schematics and found an error. On the switch assembly there are 2 resistors that are part of the tone bypass circuit R7, and R8 which should be 560 ohms. In my unit they were 39 ohms. Luckily I had a pair on hand (I figured I could change them back if it turned out that didn’t help). The change in fact improved the presentation immensely.

    I spent some time listening and felt it still wasn’t quite right so I embarked on a search through each board looking for similar discrepancies. (Not actually believing I’d be so lucky, but I figured what do I have to lose?).

    Low and behold I found several

    On the tone control assembly board (712-0001-00)

    I found 3 issues

    R1 and R2 should be 390 ohms. Mine were in fact 3.3k

    R19,20,21,22 were 3k, where they should have been 2.4k

    R23,24 should have been 100 ohms when they were 180 ohms

    On the headphone amp assembly (715-0001-00)

    I found R17,18,19,20 which should have been 47 ohms were actually 4.7 ohms

    On the equalizer amp (711-0001-00)

    R19,20 were 390 ohms rather than 330

    R17,18 were 3.3k rather than 2.2k

    For the record, I suspect this is an oddball unit. I suspect the large majority of these are correct from the factory. Also for what it’s worth , I found all the resistors I tested were well within spec of their markings usually close to 1% or better. I used 1% for all the replacements.

    I used 2 versions of S/M schematics, the original parts list and the service bulletins as the reference for my conclusions. I am aware there are frequent on the fly changes made during production and there are often errors in the S/Ms, schematics and parts lists (I was prepared to go back and I did them one change at a time).

    I’m not saying this is a good method or a cure all. I merely wanted to make this information available to someone dealing with one.

    It has in fact improved the sound of this unit greatly. I hope it helps someone along the way
     
  2. mea2112

    mea2112 AK Subscriber Subscriber

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    This would be good to post in the Kenwood/Accuphase forum.
     
  3. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    I'll see if I can get it moved. Thanks
    Move request made:thumbsup:
     
    Last edited: Aug 13, 2017
  4. luvvinvinyl

    luvvinvinyl Nikki's gone to the Rainbow Bridge. Staff Member Admin Subscriber

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  5. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    Thanks Ernie!
     
  6. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    I found the last piece of the puzzle.
    On the pushbutton assembly 716-0002-00
    R3,4,5,6
    which are described in detail on page 8 item 3 in the S/M
    3,4 should be 10k, mine are 120 ohms
    5,6 should be 1k, mine were 110 ohms
    It throws the tonal balance out.
    With proper values installed, it makes a tremendous (I'm probably grossly understating this) difference.
    I'm finally really impressed by this now!:jump:
    I'm just going to do some cosmetics on this guy now. :thumbsup:
     

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