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Thread: Crest CA18 Preamp issue

  1. #1
    Supporting Member rf7's Avatar
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    Crest CA18 Preamp issue

    I have a Crest CA18 on the bench that the top half of the waveform folds early on one channel. I swapped modules and determined that the issue lies in the preamp PCB. I checked all of the semiconductors and the resistors, and they all measured fine. The rails all measure fine. The PCB is not accessible, so I can't get a scope probe in there. Any ideas for how to chase this down?

    crest-ca18-power-amplifier-circuit-diagram.pdf

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  2. #2
    Supporting Member Jazz P Bass's Avatar
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    On a hunch I would blame it on the limit circuit.
    Specifically, the NE5517 ic.

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    Supporting Member rf7's Avatar
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    OK, I'll check that out.

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    Supporting Member rf7's Avatar
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    That was it! Thanks Jazz!

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  5. #5
    Supporting Member Jazz P Bass's Avatar
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    O/k, can I have half of the hair back that I pulled out on the one that had the same issue?

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  6. #6
    Supporting Member rf7's Avatar
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    Sorry, I can't help you with that. It is a tough amp to troubleshoot, because you can't really probe inside those amp modules when they're installed in the chassis. Thanks so much for the help, I really appreciate it!

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