MX114 power supply slump

Discussion in 'McIntosh Audio' started by mnmmt, Sep 12, 2017.

  1. mnmmt

    mnmmt AK Subscriber Subscriber

    Messages:
    88
    I have recapped my MX114, and it sounds great. I noticed that the stereo light (and stereo audio) is intermittent. Reception is always good, and the sound is strong, but on FM it usually starts mono, and then at some point Stereo (and the stereo light) kicks on. I put it on the workbench, and checked voltages. When any of the non-FM inputs is selected, the 16v power supply voltages (and all the other voltages) are spot on. When I select FM, the 16v slumps into the 10-13v range. I observed that when the voltages slump below about 12, the stereo light does not turn on, and the audio is mono. When the voltage hits 12, then stereo sound comes through and the stereo light lights up. When the MPX circuit is working, it sounds lovely.

    The 16v power supply caps were replaced with fresh Panasonic FC caps of proper uf and higher voltage rating. I also checked and replaced the 16v ps resistors that were out of spec. When the 16v power supply drops, I also see a drop in the 34v supply coming off of C210B.

    Should I suspect the Caps (C210A and B) as weak, or should I be looking for a component in the MPX or IF circuits that is sucking up too much power? Or, could this be fixed with an alignment? I've got several well-regarded Mc techs in town here for an alignment, but if the issue is not alignment related, I'd love to tackle it myself. Any ideas are welcome.

    And, thanks in advance for the help and guidance!
     

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  2. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

    Messages:
    3,068
    Location:
    NC
    Can't help but really like my 114.....good luck with it! Al
     
  3. ossidian

    ossidian Active Member

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    Location:
    47.6101° N, 122.2015° W

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