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Thread: JBL/Urei 6215 Amplifier Bias Adjustment Help Needed

  1. #1
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    JBL/Urei 6215 Amplifier Bias Adjustment Help Needed

    I have a JBL/Urei 6215 amplifier that has a bad STK2240 output chip that I am going to replace. I have a copy of the owners quasi service manual, but I cannot find any information on how to bias the amplifier. It looks like there is a bias pot for each channel, but again no information on where to connect a meter, what the reading should be etc.

    Below is a link to the manual that I have:
    http://www.jblproservice.com/pdf/Vin...5%20manual.pdf

    Any help would be greatly appreciated.

    Thanks

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    I can't help with your question, but I was told there are lots of fake STK chips for sale. My tech tried two different suppliers of STK chips in a couple of 6215s, and he said they were all fakes.

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    Senior Member Ian Mackenzie's Avatar
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    Try diyaudio.com forums

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    Quote Originally Posted by kazarkazam View Post
    I have a JBL/Urei 6215 amplifier that has a bad STK2240 output chip that I am going to replace. I have a copy of the owners quasi service manual, but I cannot find any information on how to bias the amplifier. It looks like there is a bias pot for each channel, but again no information on where to connect a meter, what the reading should be etc.

    Below is a link to the manual that I have:
    http://www.jblproservice.com/pdf/Vin...5%20manual.pdf

    Any help would be greatly appreciated.

    Thanks
    It appears that the pots offer adjustment to the DC offset circuit. See section 4.6 in the manual for a description of Q1 and Q2.

    For the amplifiers that I have working, I was able to adjust one channel that had a small offset back to zero.
    It is my understanding that most stk modules are biased internally. Let me know if you find anything different as I didn't find a clear and complete schematic for the stk-2240.

    If you can figure out the test points, the attached file has a column for typical/max quiescent.
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