New project Marantz 2250b

Discussion in 'Marantz Audio' started by pjf610, Dec 23, 2017.

  1. pjf610

    pjf610 Active Member

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    OK get back tomorrow
     
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  2. pjf610

    pjf610 Active Member

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    Hi all, I checked the voltage out J709 here is what i got:
    RC=1.7v
    LC=0
     
  3. petehall347

    petehall347 the brandy coffee man Subscriber

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    right channel has a definite problem then . matched pair of input differential transistors might fix that .
    35v supply needs fixing first though .
    left channel being 0v rings an alarm .. are you sure its not a few mv ?
     
  4. pjf610

    pjf610 Active Member

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    fluctuating between 0 and 0.001 maybe 0.003
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

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    if its on dbt the 35v may well be low
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

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    left channel bias is very high . where did you measure it from ?
     

     

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  7. pjf610

    pjf610 Active Member

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    1st I measured from the speaker output and adjusted R707, then i connected to pin 708 and 710 and adjusted R719
     
  8. petehall347

    petehall347 the brandy coffee man Subscriber

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    r719 is for idle bias . so why is set way high ? and why is offset high ?
    i guess it wont adjust ?
     
  9. pjf610

    pjf610 Active Member

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    Correct can not make adjustments
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

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    sanity check outputs emitter resistors .
     
  11. pjf610

    pjf610 Active Member

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    I will check R732 and R733 on both channels and see what I get
     

     

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  12. pjf610

    pjf610 Active Member

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    Here is the results of the R732/R733
    Right Channel;
    R732= 1.4mv
    R734= 2.3mv
    Left Channel;
    R732= 41.6mv
    R734= 43.9mv
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    in meant check how many ohms .
    are the outputs getting hot ?
     
  14. pjf610

    pjf610 Active Member

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    No the outputs are no getting hot
     
  15. pjf610

    pjf610 Active Member

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    I put a 1K resistor across R718 and was able to get the bias done between 3.5 and 3.8mv and checked the values of the H701 Zener Diode on the good channel (right side) i got 18.5 v checked the left side it bounces from .01 to.06v so i guess we have a problem their, will change it out and see what happens. I have to ask this stupid question there is a right way to install the diode how would i tell which way to put it??
     
  16. Jailtime

    Jailtime Standin' on a corner Subscriber

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    The cathode (-) end of the diode should be marked with a band, cathode is the line on a diode circuit symbol.
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    check voltage each side r713 . and polarity c702
     
  18. pjf610

    pjf610 Active Member

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    Had to replace R713 it was blown, will check, Got it with the diode
     
  19. pjf610

    pjf610 Active Member

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    OK replaced the H701 Zener diode and the left channel came to life there is a hum on it though i was able to get the bias down to 10mv but the trimming resistor is extremely sensitive and i was keeping an eye on it and it started to drop in voltage very slowly
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

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    is it a new trimmer ?
     

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