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 3000a protect light

Discussion in 'Exclusively Sansui' started by The Fuxtor, Aug 26, 2018.

  1. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    So I finally pulled out my Sansui 3000a with original packing box and some literature ! Unit is is very nice condition and I was pleased to see the service recall issue had been taken care of with factory issued mounts! Been listening to it's excellent tuner for a couple weeks but recently the unit shuts down and has the red protect light on....
    Question, I haven't looked at the service manual yet, but I assume the issue is heat related as it plays normally for a period of time until the protect comes on? Thinking about pulling the outputs and reapplying some fresh thermal grease ? I will check the bias while it's open too. Anything else to check??
     

     

    Please register to disable this ad.

  2. Tom B

    Tom B AK Subscriber Subscriber

    Messages:
    1,490
    Location:
    Bay Ridge, Brooklyn New York
    To me the bias and DC balance are the first things that need to be checked. First cold, and then when it gets hot, or when it goes into protect.
     
    slimecity and KentTeffeteller like this.
  3. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    Ok, well checking the dc offset shows about 1.2 dcv, but it appears to be a transformer coupled amp? So really it should read 0 I believe? Not sure on this... The safety mod has been done which added some coupling caps as well?? Either way I was able to adjust the bias to 25mv at the emitter resistors, the manual shows pulling the fuses but my meter has a dud fuse for measuring the 80ma there...
    At this point I am telling myself I need to recap this one, but what's the forum think??
    Charles
     
  4. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    The forum is awfully quiet.....:boring:
     
  5. ivandezande

    ivandezande Super Member

    Messages:
    1,775
    Location:
    Twin Cities
    Good to hear bias is staying fine, it still goes into protect however? Is that 1.2 volts you're seeing on the output? Or mV? It is transformer coupled, but not to the speakers, just the input to driver & output stage.
     
  6. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    Interesting setup for sure....
    1.2 dcv at output ( speaker inputs terminals)..... After 2-3 hours of use , protect light comes on and unit becomes silent!
     

     

    Please register to disable this ad.

  7. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,087
    Location:
    uk.. the middle bit
    have been looking at the protect circuit trying to see how it works ..
    looks like the scr turns the light on and mutes the inputs to the channels .. cant figure out what triggers it yet but it looks to be adjustable . i wouldn't mess with adjusting it as we dont know how its supposed to be set
    suppose you could change tr901 to see if it fixes it . doing this however may change the triggering point .
     
  8. kevzep

    kevzep Its all about the Music Subscriber

    The amplifier is by nature incredibly unstable. With that sort of DC on the output it obviously has not had the capacitor coupled mod done to the output.
    You need to go through, replace all the trimmers and then set the amp up again and see if its stable.
    If not you'll have to dig deeper.

    Forget about the protection circuit for now, the amplifier is where the problem is.
     
  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,087
    Location:
    uk.. the middle bit
    i would like to understand the protect circuit some more . as it helps me learn as to where the fault lies .or close proximity . what actually triggers it to be on ? like what is it monitoring ? yes i see there is dc at the output but cant see why it would trigger protect . i do see d901 d902 .....
    sorry if i am late to the party with this unit i am just keen to learn and help as per.
     
  10. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    Screenshot_20180828-180640.png
    The unit has the safety mods done, but looking at it , was probably done 45+ years ago. All factory clamps and same era caps used. I'll grab a pic next time I have it opened up...
    I grabbed a pic that looks similar in setup, but the the caps in my unit are the old grey caps identical to the power supply caps, the ones in the pic look more modern...
     
    Last edited: Aug 28, 2018
  11. bluestime

    bluestime AK Subscriber Subscriber

    Messages:
    3,038
    Location:
    Skagit Valley, Wa.
    There is a lot more to the mod than just those caps. There are several diodes to change or add and also some resistors.
    file:///C:/Users/Patrick/Downloads/CE007A_3000_3000A.pdf
     

    Attached Files:

     

    Please register to disable this ad.

  12. kevzep

    kevzep Its all about the Music Subscriber

    We realise this, my point was how on earth is the DC getting through the output caps.....
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,087
    Location:
    uk.. the middle bit
    might be the test equipment .. on another note what is vr803 an vr804 for ?
     
  14. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    Ok, well to further expand, I tested at speaker terminals while the unit was under a load... I had a pair of dummy loads connected... Manual asks for 10 ohm 1watt resistor but just used my 8 ohm 100 watt resistors..
    Anyone have any guidance on what/how to test more?? I can retest with another meter to double check as well .
    Oh, I just to clarify, the dummy loads were connected for biasing purposes....
    not specifically for DC offset testing
     
    Last edited: Aug 28, 2018
  15. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    They are the trimpots for the left channel.... There are 4 trimmers on this unit. Biasing calls for dialing in 80ma at each fuse holder, 2 for each channel...
    I found that as one test point was adjusted, it would pull the other test point on the channel down. I had to use 2 dmm to equal them.
    The bottom 2 pics are the DC offset measurements . I retested using 2 different dmm's
     

    Attached Files:

    Last edited: Aug 28, 2018
  16. kevzep

    kevzep Its all about the Music Subscriber

    Yeah, biasing these amps is tricky because you are adjusting each individual rail, and depending on how patient and particular you are, when you eventually get the balance right, then the DC offset will be in range.
    Best to use a pair of meters as you have found out, one channel affects the other...
     

     

    Please register to disable this ad.

  17. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    On this note, do you think 25mv is a decent target? Measuring across emitter resistors for this....
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,087
    Location:
    uk.. the middle bit
    what are vr901 vr902 for ?
     
  19. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
    2,813
    Location:
    Calgary, Alberta
    Protector circuit alignment. Screenshot_20180829-074150.png
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,087
    Location:
    uk.. the middle bit

Share This Page