Ba2000 right channel sounds very distorted

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

  1. sansuibutch

    sansuibutch Active Member

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    I've never done this before but hers what I read. This is with the negative lead of the dmm on the first letter in every test. 1490044056251-1548748500.jpg
     
  2. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Well done, those both test fine :)
     
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  3. Overundr1

    Overundr1 AK Subscriber Subscriber

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    I am going to attempt to visualize this for you, if at all unsure do not try this till we confirm what we are trying to do----
    Something just is not right if you are getting audio with no bias esp if the right channel is clean so ---
    Look at the amplifier blocks and the 4 white block resistors on each one. We want to see what kind of millivolts the outputs are actually seeing. With mini grabber hooks on the end of your meter and the meter set to dc mv scale clip one lead to lets say top left leg left side white emitter resistor and the other lead to top right leg right side emitter resistor of the same block. What we are looking for is a mv reading. Need to do this with the unit on the dbt and hook up the leads before you turn it on. If you get a reading note what it is and report back, and please please ask first if not sure what we are trying to do here.Once you get a reading we can convert that to ma values.
     
  4. sansuibutch

    sansuibutch Active Member

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    I tried this on all four sets of resistors and every set read zero mv. I'm starting to think I'm losing it and tried on 3 different meters. They all read zero. This is with no speakers hooked up and volume all the way down 20170321_073714.jpg
     
  5. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Correct method, results re-affirm the no ma values at the fuses. Will have to dig out schematic and see where things have gone awry.
     
  6. Overundr1

    Overundr1 AK Subscriber Subscriber

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    You will need to start walking he voltages back on the driver board. to find the fault
    One channel at a time---
    First verify +57vdc on pin 14 then +55vdc on pin 10
    Verify -57vdc on pin 16 then -55vdc on pin 12
    Then verify +1.1vdc on base of TR24
    Then verify -1.1vdc on base of TR22
    If voltages are present then with unit off do the six way test on those two transistors. Should be able to measure without removing them.

    Report back and we will continue.
     
  7. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    Pin 14. 0v

    Pin 10. 0v

    Pin16. +55.7v

    Pin 12. 0v


    I did notice pin 15 is the same red wire as pin 16 on the other block and also has +55.7v
     
  8. sansuibutch

    sansuibutch Active Member

    Messages:
    337

    I also have -55.9 on pin 17 and 18
     
  9. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Luv those Sansui schematics. Anyways those two voltages +55/-55 are the drive voltages to the outputs and look ok. Now measure the transistors listed above :)
     
  10. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    I don't see a tr22 but here is voltages off the 4 transistors on the heatsink.

    Tr24. .645v

    Tr26. -.649v

    Tr23. .097v

    Tr25. -.507v

    These are all taken from the base.
     
    Last edited: Mar 21, 2017 at 11:02 AM
  11. Overundr1

    Overundr1 AK Subscriber Subscriber

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    The transistors I referenced were on the driver board, not the outputs.
     
  12. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    These are on the driver board. There the biggest ones screwed down to the aluminum. Sorry about that
     
  13. sansuibutch

    sansuibutch Active Member

    Messages:
    337
  14. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Now we need voltage readings to ground all three legs on circled transistors. What we are doing is working back through the circuit towards the adjusters trying to find where the voltage drop is.
    upload_2017-3-21_15-13-21.png
     
  15. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    The last readings were from ground also.. hope that was what you were asking for. For these two these are the readings.

    Left channel. B -1.17v
    E -.507v
    C -55.7v

    Right channel B -1.14v
    E -6.43v
    C -55.7v
     
  16. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    I see that left channel is low on power on the emitter side of it. Is that transistor simply shot since it has plenty of voltage at the collector?
     
  17. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Location:
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    Start by replacing that left channel transistor then re measure :)
     
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  18. sansuibutch

    sansuibutch Active Member

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    337
    Thank you Sir..
     
  19. sansuibutch

    sansuibutch Active Member

    Messages:
    337
    I replaced that transistor and the voltage is

    B -1.10v
    E -.500v
    C - 55.5v

    I replaced it twice because I was questioning the first replacement but they are both new and similar readings
     
  20. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,041
    Location:
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    Keep working backwards through the circuit, next up take readings on the two small transistors right behind the one you tested yesterday. You are looking for the point where the voltage drops. Comparing values from the left side to the right side will keep you focused on the difference as this is a mirror circuit design.
     
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