CR-420 with left channel distortion

Discussion in 'Yamaha' started by skidmarks70, Nov 15, 2017.

  1. skidmarks70

    skidmarks70 New Member

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    So I've cleaned this guy and replaced all the capacitors in the power supply section. I thought I finally had it working and it sounded great on headphones.

    I hooked up some speakers and it initially sounded good, but I've started to get an intermittent distortion only in the left channel. It's primarily in the bass and effects both A and B speakers. If I have either (or both) sets on I can hear it on the headphones. Turning off the speakers cleans up the headphones.

    At first, cycling the power or changing the source would clear the problem for a while, but that seems to be getting less effective. I thought maybe it's a bad solder joint, so I reflowed the TR421-424 joints, but that didn't help.

    mbz posted some transistor voltages in this post: http://audiokarma.org/forums/index....quested-with-next-steps.765622/#post-10465361

    I'm going to check those next time I get a chance, but the pdf service manual I have doesn't list those? Anybody have suggestions for me?

    Thanks!
     
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  2. avionic

    avionic " Black Knights " Subscriber

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    Try cleaning you speaker selector switch. .. Maybe protect relay contacts...
     
  3. avionic

    avionic " Black Knights " Subscriber

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    It sounds more like fouled electrical contacts.
     
  4. skidmarks70

    skidmarks70 New Member

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    I haven't tried cleaning the protection relay, so that'll be first on the list. I've cleaned all the other switches a couple times, so I'd be a little surprised if that was it. But, you know a lot more than I do so I'll give it a go!

    Thanks
     
  5. avionic

    avionic " Black Knights " Subscriber

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    stand by--- Those speaker select switches would need to be disassembled to get them clean.
     
    Last edited: Nov 15, 2017
  6. ConradH

    ConradH Addicted Member

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    If I were a betting man... relay, but it might not be just the contacts. A bad cap or other part in the relay circuit can cause the relay to close with less manly vigor than needed. Check the coil voltage when the relay is closed.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

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    Yamaha's protect circuit is notorious for one or more bad caps in that circuit.Specially if they are violet sleeved.
     
  8. avionic

    avionic " Black Knights " Subscriber

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    Input Select switch may still have issues or bad solder connections.
     
  9. avionic

    avionic " Black Knights " Subscriber

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  10. skidmarks70

    skidmarks70 New Member

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    Is there a trick to getting the cap off of the relay? I couldn't see how to get into it to clean anything. I haven't taken apart the selector switches, but did hose them down and cycle them a bunch. Seems unlikely that both switches would have the same issue in just the left channel.

    The relay does have 4 violet sleeved caps nearby. I haven't checked to see what they're apart of. I may have some replacements for those.
     
  11. petehall347

    petehall347 the brandy coffee man Subscriber

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    classic relay fault . dirty contacts or bad soldering .
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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  13. skidmarks70

    skidmarks70 New Member

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    Well, I tapped on the relay a bunch and now things are working. I think you guys have this figured. I'll check out that other thread later and see if I can't clean this thing up.

    Thanks! You guys definitely know your stuff
     
  14. Chaulk61

    Chaulk61 New Member

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    I have similar issue with a cr 820 I just got. Distortion in right speaker. Very noticeable using aux and tape inputs, a little less with phono and hardly noticeable using tuner. Distortion goes away using headphones if both a and b speakers are turned off. The unit is very clean inside and I have cleaned the volume, balance, selector switches. I have also tried tapping the relay to no avail. Any suggestions?
     
  15. avionic

    avionic " Black Knights " Subscriber

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    Deoxit all your switches and controls first.
     
  16. skidmarks70

    skidmarks70 New Member

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    The noise came back on mine after a bit and tapping wasn't doing much. I still haven't gotten the cap off, but I reflowed all the solder connections on the relay and I haven't had a problem since. I think replacing or cleaning the relay is probably going to be necessary. I'm actually thinking about drilling a hole in the top of the cap and blasting it with Deoxit and then putting tape over the hole, since I don't have any scrap metal around to make shuckers. But I'm going to give it some time and see if it behaves first!
     

     

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  17. Chaulk61

    Chaulk61 New Member

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    Will do. I am a rookie at this - is there a way to clean the push button switches without taking the switches apart? Spray deoxit in from the front?
     
  18. avionic

    avionic " Black Knights " Subscriber

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    Its a crap shoot if you don't.
     
  19. Chaulk61

    Chaulk61 New Member

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    Does this relay look new?
     

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  20. avionic

    avionic " Black Knights " Subscriber

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    Can't tell for sure..
     

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