Ba2000 right channel sounds very distorted

Discussion in 'Exclusively Sansui' started by sansuibutch, Jan 18, 2016.

  1. Overundr1

    Overundr1 AK Subscriber Subscriber

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    The 2sc1403 npn are replaced with mj15003g npn, both are on the positive side (red/brown wires)
    The 2sa745 pnp are replaced with mj15004 pnp both on are on the negative side (blue/white wires)
    While you have the blocks out recheck the emitter resistors (8 total 0.3 ohm) and the follower resistors (8 total 8.2 ohm)
    Also look for any solder bridges or cold solder joints.
     
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  2. sansuibutch

    sansuibutch Well-Known Member

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    504
    Yes everything checks out. On the driver board I found one driver shorted. I'm replacing it now and hopefully I'll be up and running. And thank you so much man for taking the time to help out an amateur like me . This has been a long road for me with a lot of road blocks haaah but I am slowly learning a lot. 20170319_145205.jpg
     
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  3. sansuibutch

    sansuibutch Well-Known Member

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    504
    It now comes out of protection with every thing hooked up.. do I use my dbt to set bias? It seems to take a little longer to come out of protection than it normally does. I'm guessing because it's plugged into the dbt?
     
  4. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Set initial bias to @75ma on dbt, 100watt bulb minimum. Let it idle that way while watching bias for at least ten minutes. Adjust to 80ma no higher at this time. After this first step allowing everything to warm up connect to mains power, set to 85ma and let run for twenty minutes at idle, preferably with a towel over the heatsinks. Monitor bias and ensure it does not go over 100ma. Final setting I ended up with on mine was 95ma allowing for heating as bias is very very sensitive to thermal change.
    My BA-2000 takes about 5-7 seconds to come out of protection on mains.
     
  5. sansuibutch

    sansuibutch Well-Known Member

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    504
    Before I tried to set bias I hooked up some speakers and a tuner. The left channel is more distorted than the right ever was. I know the bias is not set but the trimmer is all the way down and it allways sounded fine before. Im trying to figure out if the problem is on the driver board. I think it might be result of the brown spade on the ps board that goes to the left channel final stage that I accidentally had a ground wire on while testing for voltage. Thers 2 wires coming of the PS board that go to the final stages. Right channel is orange and left channel is brown. When I check the voltage at the spade the orange has .35v and the brown has -.6v . I'm trying to trace that brown spade circuit but it goes to the relay and I don't know where after that. Fun fun. Or it can simply still be somthing on the driver board.. man am I stumped now
     
  6. sansuibutch

    sansuibutch Well-Known Member

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    504
    But the right channel sounds great...hahah no distortion at all
     
  7. JOMARK911

    JOMARK911 Super Member

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    There's definitely something wrong with the amp. You should get the same readings. Even a small difference. But not .35v vice -6v.
     
  8. sansuibutch

    sansuibutch Well-Known Member

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    504
    Right. I'm guessing it's from grounding that. But I noticed both of those wires that hook to the outputs also go to ground after a resistor and what looks like a choke (coil). I'm trying to figure out exactly where the power is coming from and try to assess the problem. It's hard to troubleshoot when I don't know if the power is coming or going in a particular circuit haahaa. This is confusing.
     
  9. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Lets slow down a bit and think about the amplifier circuit. There are two factors that come into play. This amp has no offset adjustment instead relying (amongst other things) on the input differential IC. Leave this fact for a moment and think about bias. The quiescent bias is required to turn on the output transistors to prevent crossover distortion which often is quite audible if severe enough. You need to get that adjusted and checked first as I indicated above.
    Now, the orange and brown wires (as I recall) carry the amplified signal out to the speaker relay and then on to the speaker jacks and require a different discussion. If you want to take the time you could hook up your dmm in dcmv range to the speaker terminals and measure the offset but until you indicate that you have adjustable bias you are just compounding the troubleshooting train of thought :)
    If you are getting two clicks, the first being the soft start relay and then the second speaker relay then I would hazard a guess your offset is pretty close.
     
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  10. Overundr1

    Overundr1 AK Subscriber Subscriber

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    And if you are at 0.00ma bias the amp is basically running off the pre-drivers and will really sound blah.
     
  11. sansuibutch

    sansuibutch Well-Known Member

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    504
    IL have to get some fusses for my meters tomarow..seems I don't have any way to check ma right now. I'd be surprised if that was the issue. I haven't turned them trimmers in a few weeks. This channel sounded fine a week ago before I blew the outputs. The trimmers are both all the way down and the right channel has no distortion and the left one I wouldn't use the word blah. Even at volume a set of headphones would put out its hard to understand what sond your listening to. I did check the offset.
    Right channel .005v
    Left channel .035v
     
  12. sansuibutch

    sansuibutch Well-Known Member

    Messages:
    504
    Both relays do click. You are correct about the orange and brown wires. They go through the speaker relay and out on the grey and blue wires. At least that's a relief knowing I didn't do any damage whIle I accidentally hooked it to ground
     
  13. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Actually you might have an issue there, if you grounded the output and powered on, the protection circuit might have saved you - but under fault conditions you may have caused excessive current to flow through the relay contacts - this will burn them and cause low and distorted output. Something else to check, the resistance of the speaker relay contacts while in the closed position.
     
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  14. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Good thought John :)
     
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  15. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I have just thought, it would depend somewhat on whether the grounding short was before or after the relay contacts - if before (as I now suspect) then the relay contacts should be OK - but if after - then what I wrote might be the case. :confused:
     
    Last edited: Mar 20, 2017
  16. sansuibutch

    sansuibutch Well-Known Member

    Messages:
    504
    I did ground it before the relay so I think I'm allright.
    I grabbed some fusses earlier and checked bias and once again it makes no sense to me.
    Right channel .05ma - .13ma
    Left channel 2.0ma - 3.73ma

    This is from starring the trimmer all the way down and going all the way up. I put a towel over the heatsinks and they never get warm. Actually they seem to be colder than room temperature. I gave the amp 10 mins idle time and they just don't warm up..
    I ohmed out the trimmers and they passed. Does this make any sense? 20170320_133435.jpg
     
  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I would check your bias control transistor(s) - the one that the trimmer is most closely connected to - sorry don't have a schematic.
     
  18. sansuibutch

    sansuibutch Well-Known Member

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    504
    I pulled these but am not exactly sure how to test them. Is it easy enough to test with a dmm?
     
  19. sansuibutch

    sansuibutch Well-Known Member

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    504
    1490036922238223413668.jpg
     
  20. Hyperion

    Hyperion Roobarb & Custard Subscriber

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