MX110 Right Channel Out

Discussion in 'McIntosh Audio' started by DrRobocop, Sep 3, 2017.

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  1. DrRobocop

    DrRobocop New Member

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    Hello all,

    Long time lurker, first time poster.

    I'm seeking some guidance regarding my MX110's non functioning right channel. Thanks to all helpful contributors and wonderful info on this site, I took it upon myself to repair my newly acquired MX110 after a local tech made a real mess of repairing the power supply.

    I am a complete amateur, but, with the collective wisdom of this site's contributors, I have been successful in re-caping the unit, and replacing the power supply on this MX110 as well as 2 other MC240s.
    The unit was functioning well after my initial repair, but I couldn't leave well enough alone. I recently swapped the 1uf capacitors and surrounding resistors at the front of the unit (the ones related to the tone control's I believe). Since then the right channel has stopped producing sound.

    Things I have tried:
    • I went back and have cleaned up and re-soldered all the connections
    • tried different caps and resistors
    • cleaned all the switches with deoxit
    • used various settings on the mode selector
    • swapped the 6u8 tubes.
    • The problem also occurs when I use the tape monitor outputs.
    Any ideas?

    Thanks in advance for your help!
     
  2. damacman

    damacman Blown and Injected Subscriber

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    A signal tracer would help you very quickly determine where the problem lies. They're not too difficult to build ...
     
  3. DrRobocop

    DrRobocop New Member

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    Thanks for your reply! I'll look around online to see about building and using a signal tracer. Would you recommend any first steps I could take with my multimeter?

    I'm hoping the problem is an easy fix (a wire without enough solder, wrong connection, etc..). Once troubleshooting goes beyond the more obvious stuff, I'm a bit lost.
    A little bit of knowledge can really get you in trouble...I've had success so far, but I hope I didn't wade in too deep and mess something up that I am completely unaware of.
     
  4. damacman

    damacman Blown and Injected Subscriber

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    You could inject a 1kHz test tone into the inputs and follow the circuit with your DMM, comparing voltages from one channel to the other. A copy of the service manual would be handy.
     
  5. DrRobocop

    DrRobocop New Member

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    thanks for the suggestion! That seems like something I could probably perform. I do have a copy of the service manual, so I'll give it a shot this weekend and let you know how it goes.
     
  6. tuberadios69

    tuberadios69 AK Subscriber Subscriber

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    I'd go back in and look at the area where you replaced the (2) 1uf @ 150volt electrolytics (with film caps I hope). They are in the audio circuit so maybe you have a cold solder joint or broken lead there(?). When I replaced those two caps in my MX110 two years ago I found it an incredibly tight spot to work in plus two resistors were taking up some real estate, too. Just a thought since you do mention until you did that, the unit worked okay.
     
    Last edited: Sep 8, 2017
  7. DrRobocop

    DrRobocop New Member

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    Thanks for your reply. I'm going to try that again first. That area is incredibly crowded, as you noted, and it's easy leave a bad connection in there. This all started when I replaced all the resistors and caps in that region with NOS allen bradleys and a set of arizona blue cactus capacitors. Those were way to large for the area and I never felt great about how I wedged them in there, or for the sound they provided. So I switched to smaller auricaps. The problem occurred after I switched to the auricaps, I may have left a cold joint, but I doubt it...I've gone over the area a few times, since then. However that is my first step this weekend.
     
  8. tuberadios69

    tuberadios69 AK Subscriber Subscriber

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    Did you sort your problem out? (hope so)
     

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