Yamaha CR 620 Distortion Issue

Discussion in 'Yamaha' started by punkzter, Jan 12, 2018.

  1. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    I gave my brother a Yamaha CR-620 two or three years ago for Christmas. At the time, it was in good working order with the exception of a popping sound when you turned it off. For better or worse, I made the call to give it to him as-is and told him that if he notice anything odd he should return it and I'd attempt a further repair.

    I replaced all of the lamps and some of the caps on the power supply before I originally sent it off.

    Fast forward to today, and he's noticed that after the unit has been on for a few hours the volume drops and gets muffled/significantly distorted. I believe that it only does this in one channel. It's hard to replicate this, because it doesn't do it every time, and it takes time for this to occur.

    Phew...so an odd problem (at least for someone inexperienced in repair work).

    I have the unit back and would like to start work on it soon. I wondered what some recommended first steps would be. I had considered just doing a wholesale recap...but I've read enough times in this forum that you probably shouldn't do that to solve a problem (you'll likely just create more in the process).

    I did a visual inspection, and it seems fine. But that's all I've got at this point. Any suggestions would be welcomed. (And, if this fixed the popping sound on turn-off, that would be fantastic!)
     

     

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  2. Bert 1100

    Bert 1100 Super Member

    Messages:
    1,167
    Location:
    Planquiri, Switzerland
    I would check the relay for a start. oxidized contacts can explain one channel going after a while, and the popping sound at shut-off could be the relay as well ?
    Just to check, remove the relay, open the top and clean the contacts with a piece of card soaked in deoxit. insert card between contacts, manually close contacts, pull card out.
    If the problem is solved, better anyway change the relay.
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,208
    Location:
    Fort Dodge, Iowa
    95% of the time popping at shut off is caused by a burnt out lamp. Shorted relay driver transistor is another possibility. But if you have a short delay before the relay "click" at power up you can rule out the driver transistor.
     
  4. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    I'll take a look at those suggestions, and check back in.
     
  5. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    All of the lamps are working. And there is a relay click at power up, so it would seem that I can rule out the driver transistor.

    I'm currently working on pulling the old relay out of the unit. I'm having a tough time, and I'm trying to be careful getting it out. You mentioned changing out the relay.

    Since I'm going through the effort to pull this out, should I just replace it now? Does anyone happen to know what the replacement part would be?
     
  6. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,208
    Location:
    Fort Dodge, Iowa

     

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  7. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    avionic likes this.
  8. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    I'm going to place an order for the relay, and I'm also going to clean out the pots. Hopefully this will resolve the issue. I'll check back in when that is complete.
     
  9. punkzter

    punkzter Brad

    Messages:
    460
    Location:
    Central Pennsylvania
    I have an update on this issue. I removed the old relay, and while I took the time to figure out how to get the cover off and did clean the contacts with de-oxit, I ultimately went the route of just replacing the thing. I didn't want to reinstall it and then have to remove it again (it was a pain to desolder it).

    The good news is that the unit no longer pops on shut-off. I guess I can attribute the pop to the relay then?

    With the cover off, I took the time to deoxit all of the knobs (volume and tone) and then the input selector area. The loudness pot was particularly noisy, and it took 3 times to get that to quiet down. The input selector switch is still not perfect, but it's much better than it was before.

    That is where I'm at. Each night when I come home, I power up the receiver and leave it on while connected to a signal generator and my scope. I'm hoping that I'll see the distortion if it occurs again.

    But I hate this type of issue, where you are kind of left hanging if you have resolved it or not. Any suggestions? Or is this just a test and wait game?
     

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