1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Sansui G-7500 Fried Resistors F2980 Board

Discussion in 'Exclusively Sansui' started by Young46, Oct 10, 2017.

  1. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Photos of the measurement from one transistor to the other on right channel.
     

    Attached Files:

     

    Please register to disable this ad.

  2. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    touch your meters probes together and deduct what you see as the readings .
     
  3. kevzep

    kevzep Its all about the Music Subscriber

    You should be measuring 4.7-5Ω from the EMITTER of the driver, to the BASE of the corresponding output transistor.

    Pictures help, like for example, I don't know why you are getting this reading, a picture can show us where you are measuring just to confirm.
     
  4. kevzep

    kevzep Its all about the Music Subscriber

    Should be reading higher than that Pete, should be about 5Ω
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    In your first picture, it looks like you are on the centre Pin of that driver, you should be on the right hand pin of the driver...
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    i am looking at it a different way yet again .. please carry on .. sorry for the interruption .. best me not bring more variables in to play
     

     

    Please register to disable this ad.

  7. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    was trying to figure the good parts from the misreading ..
     
  8. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    I'll run out and check it again. While I am doing that, attached is the same photo with some added text.
     

    Attached Files:

  9. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Here are new photos. Same reading. I was pretty sure I had it on the emitter or the driver but didn't hurt to re-check.
     

    Attached Files:

  10. kevzep

    kevzep Its all about the Music Subscriber

    Okay, thats not right, so now we have to start eliminating.

    You have to now find the BASE resistors for the output transistors, they are on the F2980 board near the emitter resistors, they will be those bluish ones with the S bends on the legs. They are 1/2 Watt. The manual states 4.7Ω, but who knows with these Sansui's, they may have changed them. Locate those and measure them, I do not think the schematic is correct for the identification numbers.
    You an measure from the end closest the output transistors, to the BASE of the corresponding output transistor, you should get something like 0.2-0.4Ω, in other-words, a direct connection.
    then from the other end of the resistor back to the EMITTER of the driver transistor.

    So we need three readings. Surrounding the BASE resistors.
    1, the resistor Ω
    2, Resistor to Output BASE.
    3, Resistor to Driver EMITTER.
     
  11. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Okay. I need to reiterate that this receiver has been worked on before I got it. I’ve stated that in earlier post but don’t know if it has been lost in the shuffle. I will check them and report my findings. Thank you
     

     

    Please register to disable this ad.

  12. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Please don't take this to mean I'm being argumentative. I am a bit confused and want to get it right so please look at this and give me some guidance. The resistors near the emitter resistors are R60 (2.2Ω), R82 (1Ω), R04 (1Ω), R66 (2Ω), R52 (220Ω), and R54 (220Ω). I'm taking the resistors you are referring to are R60, and R66. Nowhere in the area are there 4.7Ω resistors. I am attaching some marked up sheets from the s/m. I replaced R60 and R66 because R60 was reading 214Ω. Maybe I should not have, but I did. I checked them first against the s/m, measuring the actual resistors (R66 was ok but I replaced it anyway so as the match R60. I also looked up the value according to the banding on the resistor. Are R60, and R66 the resistors you are referring to and where I should be taking the measurements?
     

    Attached Files:

  13. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Missed this attachment.
     

    Attached Files:

  14. kevzep

    kevzep Its all about the Music Subscriber

    Okay, thats fine, so this means the last measurements you gave us agree with the 2.2Ω Base resistors that Sansui seem to have put in place of the 4.7Ω they show in the schematic I was looking at.
    This sort of thing is common with Sansui so lets move on. Everything is fine.

    What we can conclude from the last few measurements I had you make, is that this amplifier should work and you should be able to apply some Bias current to it.

    Turn the unit on connected to the DBT, and measure across an emitter resistor, and start winding in some bias current.
    Do not worry about the DC offset at this stage.
     
  15. Young46

    Young46 Active Member

    Messages:
    191
    Location:
    Houston,Texas
    Bias adjustment readings
     

    Attached Files:

  16. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    sorry for butting in again ..what are voltages across r72 r78 . two readings ..
     

     

    Please register to disable this ad.

  17. kevzep

    kevzep Its all about the Music Subscriber

    You should be able to adjust that down, you should be starting with the trimmer all the way ANTICLOCKWISE.
     
  18. kevzep

    kevzep Its all about the Music Subscriber

    Never start with the Bias trimmer in the middle.
    Only start the DC offset with the trimmer in the middle.


    He has 100Ω emitter resistors in there at the moment. That is why the voltage is that high.
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    What you have there is 290mA of current, you need to adjust it down, way down....
    I would like to see you be able to adjust it down to about 3VDC
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    ah ..i missed that bit .. even so knowing each voltage to see if a relative match isnt a bad idea to see ,.
     

Share This Page