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Fender Passport pulsating problem

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  • #31
    Originally posted by Enzo View Post
    36v means 72v could be across each. so 200v is roughly twice that, a margin I like myself. I don't know where 900 volts would come from to threaten those devices.
    i think that was the lowest voltage I found where the other specs were met.

    nosaj
    soldering stuff that's broken, breaking stuff that works, Yeah!

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    • #32
      Looks like audiolabs it is. Thanks everyone for helping out!! I should of asked in the first place. I looked for a sub for a while and gave up. This is the first time ordering bad parts for me. Lesson learned.
      I'll let you know how it goes.

      Thanks again!!

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      • #33
        Ok so, my guy needs this in a week. The mosfets should arrive by then, but I have a question about something I would like to go over first.

        There is DC offset protection from an op amp. How can I test the op amp?

        Here's what the service manual says about it.

        Speaker short circuit protection is provided by
        U203B. This is accomplished when the output is
        shorted to ground, the normal differential signal ap-
        plied to U203B is absent at the negative terminal
        while at the same time, the second stage is now
        forced into open loop gain. The drive signal is inte-
        grated into C211 forcing a positive voltage at the
        output of U203B that pulls the gate of FET Q207
        into conduction from its previous negative bias off
        point, nulling the output of U203A. With the output
        of U203A minimized the output current of the ampli-
        fier is minimized until the short is removed. At this
        time, C211 will discharge allowing normal operation
        of the amplifier. Note: Some small DC offset will be
        present when the amplifier is in the short circuit pro-
        tect mode.

        Pg 27 is the amp schematic where this is located.
        There is no DC on the speaker.

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        • #34
          The parts from Audiolab came in yesterday. I put them in and it works great again!

          Thanks for helping with the parts locate!!

          My initial thought was the outputs are bad. The bad parts from eBay made me start thinking something else was wrong. Once again, I should of asked here first for parts cross reference.

          Thanks again to all!!

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