Sansui g-5700 tuner bad

Discussion in 'Exclusively Sansui' started by Tomcow, Dec 31, 2018.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Make sure after changing that resistor that you power up 'on DBT' and also set yourself up to monitor bias current (for the faulty channel) from the word go. As you will have adjusted the bias current with those low voltages present due to the faulty resistor, so will very likely need turning down promptly after power on. ;)
     

     

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  2. Tomcow

    Tomcow Active Member

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    Ok thanks.I will post as soon as the resistor arrives.
     
  3. Tomcow

    Tomcow Active Member

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    Put new resistor in.Get 0mv dc at pins 85 and 86 to ground.Left channel,pin 85 to blue wire,adjusted to 3.3mv,pin 86 to blue wire on right channel,Adjusted to 3.3mv.Still no relay on.Noticed when I turned trim pot on right channel for dc adjustment,couldn’t get meter to change on the dc millavolt reading.
     
  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Those two statements....So you couldn't adjust DC offset away from zero for the right channel is that what you are saying? - I suggest you have a faulty trimmer - possibly broken solder joint?

    How is the DBT looking? - what's the bulb doing?
     
  5. Tomcow

    Tomcow Active Member

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    That is correct.pin86)right channel,dc adjustment,pin to ground,reading doesn’t change when turning dc trim pot.Other side(85 pin to ground)adjusts fine.Both the other trim pots( for bias adjustment)adjust fine(3.3mv,pins 85 and 86 to blue wires on each channel).Bulb dimmer is dim.
     
  6. Tomcow

    Tomcow Active Member

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    Tr-05,Tr-06,Tr-07 and Tr-08 all read around 35v on emitter to ground.Tr-08 reads.72 V collector to ground,Tr-06 reads -35 Volts collector to ground,Tr-05 reads -35 Volts collector to ground and Tr-05 reads 1.13 Volts collector to ground.All pre-drivers,I get 36.8 Volts,collector to base on both 2sd-357 and -36.8 Volts on both 2sb-527’s.
     

     

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  7. Tomcow

    Tomcow Active Member

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    All 4 trim pots are brand new Bourne’s.
     
  8. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Check your soldering and how you have connected the trimmers, is it possible you may have misplaced a track leg with a slider leg? or something similar?

    Have you recently changed the first set of (wrong orientation) replacement Bourns trimmers?

    Remove the offending trimmer and check that it actually adjusts when connected to an ohm-meter?
    Double check the adjustment test points to make sure your mini-grabbers are making contact?
     
    Last edited: Jan 12, 2019
  9. Tomcow

    Tomcow Active Member

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    117
    Ok.I checked pin 85 to ground,got 1.2V.Was able to adjust Vr-1 down to 0mv.Pin 86 to ground,got 2.0V.Adjusted Vr-2 right down to 0mv.Vr-3 and Vr-4 are reading 0mv and cannot adjust(nothing changes when I turn them when measuring from pin 85 to blue wire and pin 86 to blue wire on right side.
     
  10. Tomcow

    Tomcow Active Member

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    Cannot figure it out.No relay and also noticed the big transformer is dead silent.Don’t they usually have a slight hum??
     
  11. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    A slight hum is normal - but you would have to be in a very quiet room to hear it.

    So, you are now unable to adjust bias on both channels, have you checked that you are getting power to the OP transistors? - and haven't blown a fuse somewhere?

    Note also there is an error on the schematic that has been pointed out to me - "Jumper pin #59 should be #85" - (thanks Steve ;)) - have a look at that and see if you can make sense of it from what you can see.
     

     

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  12. Tomcow

    Tomcow Active Member

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    Ok.I will check that out
     
  13. Tomcow

    Tomcow Active Member

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    3,2amp fuses all good.1 6 amp fuse,good.Where can I measure next to test voltages?Tom
     
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Take a look at the schematic, you'll see pink ovals with voltages noted in them - check all these and report back, particularly check the '+' and '-' 54V on the collectors of the OP transistors. ;)
     
  15. Tomcow

    Tomcow Active Member

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    Output transistors,Right channel,37.6 volts on emitter of 1105.Same side,I think is 2578,-37.5 volts.Left side,same readings as right side.Test was done on BD.quick check at full power netted 53V
     
    Last edited: Jan 12, 2019
  16. kevzep

    kevzep Its all about the Music Subscriber

    None of this makes sense, this is all contradicting itself.

    If you can adjust the DC offset down to 0mVDC then the relay will pull in and the green "safely operate" indicator will come on. Job done, but this is not happening.

    You are saying 0mV on the output for DC offset, then you say there is 37 volts on the output transistor emitters, this is impossible if you have 0VDC offset.

    Are you measuring in the right place?

    Can you not attach directly to the emitter resistor to measure the Bias?
    Can you not connect directly to the amp side of the relay so you know you are in the right place for DC offset?

    Personally I think you are not measuring in the right place and this is why nothing makes sense.

    Are you on a DBT? ​

     
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  17. Tomcow

    Tomcow Active Member

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    I thought you said dc is set connecting pin 85 and ground,left channel and pin 86 to ground right channel?When I do this and adjust Vr-1,for the left channel and Vr-2 for the right channel,I can adjust down to 0mv dc.Then I thought you said for bias,pin 85 to blue(A) left channel and pin 86 to blue wire (B) right channel?
     
  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I just so happens that pin 85 & pin 86 to ground are the points for measuring DC offset for the two channels - BUT also pin 85 to blue wire, and pin 86 to blue wire are the points to measure for bias on the two OP transistor PCB's.

    Pins 85 & 86 are the centre points of the dual emitter resistors, and I simply could not understand why when it worked before, you suddenly couldn't set the DC offset. :confused:

    (Thanks are due to Kevzep for his post above for adding some considerable clarity to a problem which has been baffling me - that's for sure. ;) )
     
  19. Tomcow

    Tomcow Active Member

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    I’m about to give up.Its probably something fairly simple but this whole layout is confusing to me.I have 2 big Pioneers(sx1010,1050)plus a big Fisher that all work great and are easier to work on than this one.
     
  20. Tomcow

    Tomcow Active Member

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    Last thing.Where can I check dc before the relay?Maybe that will shed some light on this.I can’t measure dc at the speaker terminals because the protection circuit is engaged
     

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