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Sansui G-9700 HELP!

Discussion in 'Exclusively Sansui' started by lambord, Aug 15, 2018.

  1. lambord

    lambord Active Member

    Messages:
    126
    I am not sure if this is how the circuit is run but does it got in order of number? So R01 comes before R02 and then goes R03? Or is it just random? If they go in order, I was checking board to board in order, everything was the same up until R17. I pulled R20 as well and on the left side is open and right side is 6.82 k ohm.... not looking too good lol
     

     

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  2. petehall347

    petehall347 the brandy coffee man Subscriber

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    i was being on the cautious side and it is something to do whilst waiting on the parts to arrive . cant really do any harm can it ?
     
  3. kevzep

    kevzep Its all about the Music Subscriber

    One thing at a time for these guys who do not have a lot of knowledge and experience......There is only one thing to do when the resistors arrive, then we can see how the amplifier is performing without a number of "other things" which have been done in the meantime.
     
  4. lambord

    lambord Active Member

    Messages:
    126
    I have made the DBT too, should the DC offset and bias be turned down before powering on with new resistors?
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

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    no problem . was just covering unexpected things .. p.s met the op on here a good while ago . another G that worked for more than a few seconds .
     
  6. kevzep

    kevzep Its all about the Music Subscriber

    This model is pretty reliable and is a good design, its not too bad to work on and I have found them easy to repair...
     
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  7. petehall347

    petehall347 the brandy coffee man Subscriber

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    phew .. not like the the one i hope is still on hold ..,
     
  8. lambord

    lambord Active Member

    Messages:
    126
    I think your refering to our previous encounter Pete. Haha, the G-5700 has been sold for a couple years to a person that planned on fixing it. I moved on to bigger and better units:)
     
  9. petehall347

    petehall347 the brandy coffee man Subscriber

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    well done .. i do remember it briefly working then it went pop . we all know more since then for sure .. like i said back then would happen .
     
  10. lambord

    lambord Active Member

    Messages:
    126
    Received the resistors and they are all soldered in, all measuring about 150 ohm in the circuit.
     
  11. kevzep

    kevzep Its all about the Music Subscriber

    You should be able to fire it up and set the bias now...
     

     

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  12. lambord

    lambord Active Member

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    126
    I tried with the dim bulb and as i turn the VR03, the light becomes brighter and brighter until the relays or something switches and the "safely operate" light starts blinking...... also the first time I tried touching TR02 and TR03 I shorted something because a large arch roasted my multi meter probes, then I put on the covers I should have put on the first time:(
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    So what happened to turning it on and setting the bias?
    Why are you probing TR02 and 03, thats not part of the procedure?
    Do you have the service manual? Are you following the instructions?

    If something arced, you have now blown some transistors.
    These will now need to be replaced.

    VR03 is the bias trimmer, increasing the bias will make the DBT brighter as the circuit is drawing more current.
    You should be measuring the bias as you adjust the trimmer as per the instructions to set it at the correct mV as outlined in the manual, NOT just turning the trimmer to "see what happens".

    You need to remove the transistor which arced, and test it, you need to test surrounding transistors as well and make sure nothing else was fried.
     
  14. lambord

    lambord Active Member

    Messages:
    126
    I was performing steps 3 and 4 in this picture of the service manual....."measurement output between terminals of TR02 and TR03"
    upload_2018-10-30_16-23-22.png
     
  15. petehall347

    petehall347 the brandy coffee man Subscriber

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    the emitter resistors are the same connection electrically and better to clip leads on there . less risk of shorting stuff out .
     
  16. kevzep

    kevzep Its all about the Music Subscriber

    Okay I thought you were measuring on the driver board, you didn't say what board you were on.
    Well okay, you've most likely taken out the output transistors.
    Thats not ideal!
    Note where it says BEFORE you turn the power on....
    You should be using mini-grabbers.

    Pete, I don't think you can get to the emitter resistors which is why they have you connect to the emitters of those transistors.
     

     

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  17. lambord

    lambord Active Member

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    126
    Yeah sorry I did not specify the board I was measuring. I was following the service manual and I also turned VR03 all the way down before powering on.
    Just to be clear, I should be doing this adjustment with the dim bulb? That is just kind of a safety device for a short?
    I will start disassembling to get to transistors, should I just google how to test a transistor?
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

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    must admit i cant remember looking at one in the flesh so to speak.
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    No, it needs to be off the DBT when setting the bias, as the DBT drops the voltage and limits the current. The settings need to be done at full AC line voltage.

    You most definitely need to know how to test a transistor to carry out the necessary repair.
     
  20. lambord

    lambord Active Member

    Messages:
    126
    Ok I will look up on testing the transistors. here is the board layout if your curious Pete. The last picture you can see where the short was
    [​IMG][​IMG][​IMG]
     

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