4100 power guard issue

Discussion in 'McIntosh Audio' started by Kralcster, Sep 4, 2017.

  1. Kralcster

    Kralcster New Member

    Greenwich CT
    Was having left channel issues. Replaced speaker relay and had some improvement but not total. Used DeOxit and things seemed cleared up, but today left channel cut out pretty much entirely and left channel Power Guard LED is lit when any power is sent to the speakers.

    Anyone have any ideas at this point?


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  2. c_dk

    c_dk Addicted Member

    West Michigan
    Sorry about leaving you hanging out there but have been busy with issues.....

    PG indicates that the amp is putting out distortion in excess of 1%....it will try to lower the input into the amp section to lower that distortion but it can only do so much.....

    The power supply sections of these 70's units are failing regularly so all should be recapped now as a matter of coarse but most often that will cause issues in both channels.....I suspect a failing predriver transistor if it is truly in only one channel.

    It should be on a tech's bench.......

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