Piano, Organ, and Keyboard/Organ Buzz

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Question
Hello, I have a Story and Clark organ which has been making a horrid buzzing when I turn it on. I have checked all the wires and everything is connected, as I initially thought it be a grounding issue. I unmounted the power unit and found a blown capacitor and replaced it, and it still buzzes. However, if i unplug the 6"x9" CTS speaker and Leslie, it works fine- the other speakers play fine, just quietly. There is nothing else I see that is visibly wrong in the power unit or organ- no bubbles, varnish, everything is soldered correctly, etc. I tested a second speaker I know works and it gives the same issue.

The organ is a S&C 250 model. Any help would be appreciated

Answer
Hum comes from 2 possible sources: 60 cycle AC or 120 cycle DC ripple.  A bad ground is a typical problem, and as you probably know, a bad filter capacitor that is no longer filtering the ripple out is another common problem.  You say you replaced one capacitor.  With a hum problem, I suggest you replace all the filter caps since they are all nearing the end of their expected life.  The other common problem is the rectifier.  It is usually an array of 4 diodes.  If one of them were to go bad, hum would be present and difficult to mask.  

Piano, Organ, and Keyboard

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Thomas Britanyak

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I am a full time organ/piano technician who has been actively involved with the design, building, repair, maintenance and installation of organs and pianos for 35 years. I began as a keyboard instrument apprentice and hold degrees in music and electronics. If you need a piano's date of manufacture, please go to http://www.pianoexchange.com/howold.htm or http://www.bluebookofpianos.com/pianoage.html I am happy to answer musical or technical questions, however, I CANNOT offer appraisals on pianos or organs. Please do not ask what an instrument is worth. For this service please contact an experienced local appraiser or try the following links: https://mmm1100.verio-web.com/blueb1/appraisal.html or http://www.57piano.com/questions.htm

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I am a full time organ/piano technician who has been actively involved with the design, building, repair, maintenance and installation of organs and pianos for 35 years. I began as a keyboard instrument apprentice and hold degrees in music and electronics.

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I am a full time organ/piano technician who has been actively involved with the design, building, repair, maintenance and installation of organs and pianos for 35 years. I began as a keyboard instrument apprentice and hold degrees in music and electronics.

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