2235B Pop on switch off

Discussion in 'Marantz Audio' started by VintageMad89, Mar 14, 2017.

  1. VintageMad89

    VintageMad89 Active Member

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    Hi folks, I have a small problem when powering off my receiver. Basically when I release the power switch, I get an audible 'pop' through both speakers (on any input or volume and speaker A or B)

    It has always done this in the 2 years I've owned it but the problem persists even after a full recap and relay burnish...

    I'm thinking perhaps a relay driver transistor may be going bad?

    Any suggestions would be great!

    Scott
     
  2. Leestereo

    Leestereo Super Member

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    Your symptoms point to an output DC offset rather than a relay circuit problem.
     
  3. VintageMad89

    VintageMad89 Active Member

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    Sorry, I forgot to mention that Bias & Dc offset have been adjusted as per the service manual
     
  4. Leestereo

    Leestereo Super Member

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    If the speakers don't "pop" on turn on, but only on turn off, it may be that the DC offset drifts as the unit warms up.
     
  5. bktheking

    bktheking Gitter Done!

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    Relay drive transistor merely energizes the coil to close the relay, nothing to do with audio. Sounds like dc offset which can drift if the differential pair gain is out of whack. Have you replaced the differential pairs?
     
  6. VintageMad89

    VintageMad89 Active Member

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    Thanks for the suggestion, I have measured offset after 30 mins and both channels stay around +-1mV between switch on and warm up so don't appear to be any problems there.
    I have also tried some deoxit on the power switch (just in case) with no improvement.
     
  7. VintageMad89

    VintageMad89 Active Member

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    That, I have not done. Are they on the power amp board?
     
  8. bktheking

    bktheking Gitter Done!

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    Yes. As well, try shorting the main in jumpers and see if it does it. Transistors in the pre can get noisy causing issues in the main amp(s).
     
  9. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    Could a poorly functioning snubber cause this? :dunno:
     
  10. VintageMad89

    VintageMad89 Active Member

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    Thanks, I'll try that also!

    Pardon my ignorance, but do you happen to know where the pairs are on the board? I have the schematic in front of me...
     
  11. Leestereo

    Leestereo Super Member

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  12. VintageMad89

    VintageMad89 Active Member

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    Great, thank you Leestereo! I will pull and test them and report back. I know it's not a huuuge issue as the unit performs well, but you know what these little "gremlins" are like...
     
  13. bryans12v

    bryans12v Marantz Junkie Subscriber

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    I would also take a peek at the relay contacts. They could probably use a burnish/polish.
     
  14. VintageMad89

    VintageMad89 Active Member

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    A quick update-- I haven't got round to removing the differential pairs (that's tomorrow's job!) but looking at the power switch again, I've noticed there isn't a suppressor cap across the pins. Should there be?

    Regards
     
  15. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    Some units have it at the back where the power cord enters - usually around the unswitched outlet or wherever the ends of the power cord connect.
     
  16. VintageMad89

    VintageMad89 Active Member

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    UPDATE

    So, here goes. I have replaced both diff pairs on the amp board and still, the POP remains.

    I can't seem to find the suppressor cap Steven was talking about- the only thing I can see that resembles this is in the attached picture

    I'm not sure what it is the orange disc cap is connected to, maybe someone can shed some light on that, thanks.
     

    Attached Files:

  17. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    You are looking for something similar to this blue cap+resistor. It's either on the power switch or in the back near where the power cord comes in.

    [​IMG]
     
  18. VintageMad89

    VintageMad89 Active Member

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    Thanks Steven, unfortunately there is nothing that resembles the picture. Similar or otherwise.
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

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    check h812 then if ok replace caps in relay circuit .
    at a guess the relay isnt releasing fast enough
     
  20. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    It's probably a long shot that this is the problem anyway. But it is shown on the schematic as G001 across the power switch, S001 (although it could still be mounted in the back.). I wonder if it is missing? :dunno:
     

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