CR-620 sometimes coming out of protection to early causing speaker thump

Discussion in 'Yamaha' started by Eastham, Apr 14, 2018.

  1. Eastham

    Eastham More Class-A than ever!

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    So my 620 has now started coming out of protection to early causing a negative spike at the speaker terminals, it happens from a cold start after it's been off for a while or if I turn the receiver off then back on after a second.
    When it comes out of protection normally it takes around 3.5s for the relay to close when it opens to early it takes around a second to 1.5s to close.

    Voltages at TR809 are as follows:
    Base: 21v while relay is open, 12.5v after the relay closes
    Collector: 0v while relay is open, 13.22 after the relay closes
    Emitter: 21.5v while relay is open, 13.28v after the relay closes

    Any ideas what I should check?
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    Reflow the solder connections for TR808 and 809. If that doesn't help replace them.
     
  3. avionic

    avionic " Black Knights " Subscriber

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    Let me try to get this right. You turn on the unit. It normally takes 3.5s for the relay to click? When it acts up it clicks at about 1.5s.? There should be no delay at power down , It should instantly open the contacts at power off.
     
  4. Eastham

    Eastham More Class-A than ever!

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    Yep and instant off.
     
  5. Eastham

    Eastham More Class-A than ever!

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    I replaced TR808 with a KSC1845 and the flyback diode for the relay with a 1N4001 to no avail. I've ordered a KSP2907ATA to replace TR809 which is a 2SB544. I also went around the power supply, amp and protection circuits touching up all the solder joints again for good measure.
     
  6. avionic

    avionic " Black Knights " Subscriber

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    Have a close look at C815 and 816 as well. Especially C816 small violet colored 33µf/16v. These are quite often -- bad --.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

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    I have never in 40 yrs found a bad relay flyback diode.
     
  8. Eastham

    Eastham More Class-A than ever!

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    I gave this receiver a full re-cap about 2ish years ago, I used Panasonic FC type capacitors.

    I think I'll probably end up re installing the original flyback diode, it's probably better suited for the job.

    Things that may be worth noting, I did change the original filter caps out for higher value 10,000µF Vishay caps, I've also replaced the protection relay with a Omron MY2N 12DC(S) as the contacts on the original relay where fubar despite this unit looking like it'd never been used but the problem was there beforehand, I was hoping replacing they relay would stop the thump.
     
  9. avionic

    avionic " Black Knights " Subscriber

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    Good to know..Well lets hope the relay driver TR809 does the trick.
     
  10. Eastham

    Eastham More Class-A than ever!

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    I think I may have found the issue... I think If my guessing is correct, I've replaced C815 with a 47µF instead of a 4.7... Is C815 located directly below TR807 by any chance?
     
  11. Eastham

    Eastham More Class-A than ever!

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    I'm such a tool, looks like it was the problem after all... I'm gonna let the receiver sit for a half hour and see if it thumps when I turn it on but so far everything seems gravy... I think I need to get my eyes checked... Thanks Avionic!
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    Little cap closest to TR807 is 4.7µf/35v verified on a parts unit I have here.
     
  13. Eastham

    Eastham More Class-A than ever!

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    Yep, I put the wrong cap in when I re-capped it. Wonder why I never noticed the thump before, everything seems fine now. Relay always takes over 3 seconds to click and no more thump.
     
  14. avionic

    avionic " Black Knights " Subscriber

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    Great discovery..Alls well , that ends well.
     
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  15. Eastham

    Eastham More Class-A than ever!

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    Indeed, thanks again for the help. Another problem in my CR-620 that was my own doing... Now fixed!
     

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