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Attention M3 Electronics Gods... HELP!

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  • Attention M3 Electronics Gods... HELP!

    Ok... so I'll quit using the quote buttonto type posts... lol :).... so I still have this horrible hum coming from my M3.... it goes through my Leslie cable to.. it's has to be either the amp or the vibrato scanner... the brownish/orange pads under the wire washers ARE moist... does that mean the scanner needs cleaning and is causing this upperbass/midbass hum? I read a post earlier about shorting out the caps in the vibrato line box.. how is this done? I have a Heathkit IB-5281 RLC Bridge.. can I use this to somehow test the R's/L's/and C's? HELP!

  • #2
    Re: Attention M3 Electronics Gods... HELP!



    Hum is usually from bad filter caps in the amp chassis. It could be a loose wire somewhere, but not as likely. As for the scanner, not usually the source of hum. The moist fiber washers indicate the scanner has been over oiled at some point. The usual symptom is a vibrato that is choppy, or even a choppy thumping when not playing it, or a weak vibrato. I'm sure a scanner rebuild is in your near future. [:)]</p>

    I test filters in circuit with a meter. looking for any AC voltage on the DC lines. A very quick way to find a bad cap is to parallel a good cap across each one in the amp, one at a time. Turn off the organ, clip a good cap from ground to a point in the amp where a filter is, (Observe the polarity) , turn the organ on and see if the hum is still there. Be sure to leave the new cap connected until you have completely powered down. Simply un-clipping it with the amp on will leave that cap fully charged! </p>

    Once you find it, you can disconnect the old cap and solder in the replacement. Some even solder a new one right to the old one. It's more common for an old filter to just open up. In that case, a new one soldered to it is no problem. However, in some rare cases, a filter can short to ground. This would not hurt the new cap but you are leaving a potential problem under the chassis if the old cap is not removed. (electrically) </p>

    George
    </p>

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    • #3
      Re: Attention M3 Electronics Gods... HELP!



      Thanks George :)))) Ok.. I've read through your reply very carefully.... </P>


      You say filter caps... so in other words I need to get spares for every value of capacitor used underneath my AO-29? Could it be that big metal can capacitor.... the dry cell electrolytic thing? I guess I'll need to document all the wires soldered to the terminals on the amp.... looks like someone spliced in a whole new amp at some point in my organ's life... I've got two different schematics of the M3 though.... a big one I've tacked to my wall and another on file here on my computer... between the two of them I should be able to get it all documented..../actionbreathes... and IJUST started getting inspiration for some music..hahaha.....in the future I think I'll go with spade connectors for the termninals... I know that doesn't get close to a solder job but for ease of servicing......</P>

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      • #4
        Re: Attention M3 Electronics Gods... HELP!



        If you try the quick clipping a new cap over the old one routine, just get a 47MFD @ 450V. You can use it on most filters for a test. Yes, the filters are the large cans.</p>

        George
        </p>

        </p>

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        • #5
          Re: Attention M3 Electronics Gods... HELP!



          Mannnn......</P>


          Guess what it was? I had just happened to notice how poor the soldering was on the amp and checked the wiring with my schematic from Captain Foldback's site... and there it was.... some idiot had a short wire connected from X to BK/C! It sounds wonderful now!!! What the hell was that tech thinking? All that wire did was create noise.... now I can barely hear the generator spinning!</P>


          </P>

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          • #6
            Re: Attention M3 Electronics Gods... HELP!

            It looks like he was trying to put a DC bias on the vibrato scanner... Could he possibly have been trying to do this to overcome the problem of dendrite whiskersthat can form and short the scanner? Certainly not a very good plan...

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