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problem with the performer 650

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  • problem with the performer 650

    This amp came in completely fried and beaten.
    Because of a very higher value fuse replacement, all the power amp section was gone badly: power transistors, and all of the diodes and zener diodes around it were physically broken.
    Now the funny thing that's driving me nuts is that I have good signal at pin 1 in U4A, good signal at pin 6 of the U7, good signal in both power transistors, BUT just a tiny almost inaudible signal at the speaker connectors.
    If I plug the signal generator in the effects return, same thing, so the problem is definetely not in the "preamp".
    I have ckecked all components around the power section and all appear ok or have been replaced for good ones.

    And here I am... completely lost once again.
    Any help?

  • #2
    Compare the signal at pin 6 of U7 to the junction of R96 and R97. It should be about the same amplitude. If the darlingtons blew they most likely took out the emitter resistors. This may be a stupid question but did you check the speaker for damage.

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    • #3
      Originally posted by Twist View Post
      ...If the darlingtons blew they most likely took out the emitter resistors. ...
      And they did.
      They could be about the only components in the whole amp that I didn't check.
      They had continuity, yes, but they had drifted to 130K or so.
      I owe you a few beers now.

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      • #4
        Glad you got it going. I've done the same thing before.

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