C2a volume fade in one channel

Discussion in 'Yamaha' started by jdsalinger, Aug 11, 2018.

  1. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    I have thoroughly de-oxited switches and pots and replaced all electrolytics.

    Once in a while though, the RH channel will drop out temporarily and last night it kind of faded out slowly. But then the channel popped back after 15 sec or so.

    It seems to happen when the amp is first started up and then gets better after warm-up, but it hasn't happened enough to say for sure and once I just disconnected it and went through the M2 directly from my DAC. So I know it's not the M2.

    I realize this is a complex preamp and it could be anything. But just wanted to ask before I dig in. Is this perhaps a common issues with Yamaha preamps? Is there a recommended faulty transistor or relay that I should have replaced in addition to the recap?

    I don't think I experienced this before the recap, but I didn't have it long before recapping either.

    TIA !
     

     

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  2. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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    This problem could be ...
    1. A cold solder connection in the R-channel signal path.
    2. A faulty transistor in the R-channel signal path. ( breaking down as the component heats up)

    It may be a tough problem to locate. Due to it being so intermittent.
     
  3. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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    What source were you using when the last episode occurred?
     
  4. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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    Have you eliminated the possibility of the source or the power amplifier being the problem?
     
  5. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Streaming Spotify through a new Topping DAC. Aux input.

    Yes, First time I noticed it, I took the C2a out of the system and went directly into the M2 from the Chromecast Audio. No more issues.
    That time, the channel had some soft popping, squealing sound too if I remember correctly.

    I seem to recall that there are many "Another thread about crackling and popping". Maybe it's my turn. I will search for those threads and see if I can narrow it down.
     
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  6. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    I looked really hard for any cracked solder joints when I did the recap. Everything looked really good. But looks can be deceiving.
    I'm kinda glad it's in the C2a and not the M2 cause it should be easier to work on and diagnose.
     

     

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  7. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    While I hunt for the problem, I'll add that yesterday, I heard what sounded like a very faint squeal with a "vinyl record scratch" tone to it. It sounded like the sound effect they played when the professor from Gilligan's Island was trying to tune in their radio. :rolleyes: :thumbsup: Only lasted a brief second or two and like I said...almost inaudible.

    IME, a failing transistor would just cut signal or make a loud crackling (I had a transistor fail in a Marantz 2230. Horrible, loud crackling sound). Could a failing transistor make a sound like that?

    I'm leaning towards a cold solder joint because, although I didn't listen to the C2a for long before recapping, I think I would have noticed this at some point. It happens at least every other listening session.
     
  8. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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    Yes
     
  9. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    Thanks. Now to figure out which of the 30+ transistors is mis-behaving. :rolleyes:
     
  10. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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  11. jdsalinger

    jdsalinger AK Subscriber Subscriber

    Messages:
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    I opened up the C2a to fix a bad ground to the Tuner and Aux inputs. I had to solder a bus wire from the tape input jacks and THEN run a wire from the bus to the pin that is part of the connector from the pin jack board to the EQ board.

    I also just discovered that Phono 2 doesn't work at all because the positive and ground are shorted together on the pin jack PCB. I tried de-soldering all of the pins and checking for continuity, but all pins are still shorted together. This bugs me because even though I can listen to phono1, according to the owners manual, phono 2 is specifically for MM carts.

    Lastly, the 47K and 100K cartridge load positions don't pass any sound. I don't see any broken or cold solder joints, so I'm assuming something is disconnected inside the 6-6-63 "controller" pot.

    This thing will be torn apart for a while cause I'm planning on replacing resistors as PM and because I'd like to start to attack the subtle channel fade and (rare and itermittent) squeal issue
     

     

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  12. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

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    They're not supposed to. They are for plug-in cartridge load plugs.Read the owners manual about cart. load plugs.
     
  13. milo63

    milo63 “Talent is a pursued interest." Bob Ross Subscriber

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    Hey my C-2a peeps!
    I scanned the schematic from my owners manual up to my Google Drive (380GB), if anybody wants it just IM me your email and I'll give you access.

    @Komodo @jdsalinger @lowredmoon @mr.muddles @OMGCat!

    Mine has issues post recap (38V on TP1) but I'm not ready to ask for help yet, trying to self-educate myself.:rockon:
     
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  14. jdsalinger

    jdsalinger AK Subscriber Subscriber

    Messages:
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    Location:
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    Sorry for the confusion Avionic. I misspoke. What I meant was the impedance selector knob on the front face.
    On phono 1 input, I get no sound using the 47K & 100K selection ( I understand that 100K is for LOMC only, but I would think I'd hear something )
    With phono 2, I just discovered that the selector knob should be on 2/47k. I never tried that (and now the C2a is torn apart for a re-resistor job)

    I can't figure out how my phono 2 inputs got shorted to ground. There was no evidence of a solder touch up, but sure enough, there is continuity between R&L and their grounds.

    milo63, I would like access to your GD please! You have my email. Thanks.
     

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