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Allen MOS-1 DM capture action problem

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  • Allen MOS-1 DM capture action problem

    Hey gang, I had the following problem with our S301B Allen: one stop wouldn't capture on any piston, and would in fact turn off even if it was already on and was supposed to stay on (it was set to be "on" with that particular piston). I asked John Bird for advice via a PM, and as usual he was spot on- problem solved! With his permission I'm passing on his reply in case it's useful to others who may have the same problem. Regards to all, Bill Miller

    [I]Hi Bill,

    Check the stop bracket leaf switches. Two little bent-inward metal leafs that make contact with the central tongue when the tab is turned on. One goes to the stopboard array to activate the stop, the other one goes to the capture action sense connection. If the sense connection is not making good contact, the stop will always set in the "off" position, giving the symptom you describe.

    Even if the leaf appears to be making contact with the tongue, there could be some gunk in the way that keeps it from having solid electrical connection. Also, trace the wire from the contact leaf to the capture board. It will terminate on one of the divisional plug pins. I suppose there is a chart somewhere that tells where each stop's sense wire goes on the DM board, but I don't have that at hand. You can trace it with a meter. Try the stop right beside it and trace to one of the pins on the DM board, then do the same with your Octave 8.

    Other than that, I don't know of anything that would keep it from setting. Of course, the stop bracket itself contains a couple of steering diodes and maybe a transistor (?) that determine which coil gets the pulse when the capture fires. You might have to remove the bracket and check those if all else fails. It could also be a fault on the DM board, but that would be a strange one. There are unused pins in each division, so if the problem turned out to be on the DM board, you could move the sense wire to a different pin, then move the corresponding "fire" wire to the output that corresponds to the new sense pin. That would require a chart for sure.

    John

  • #2
    Glad that I could be helpful to you, Bill. Those rather flimsy little contact leaves can cause any stop not to sound when drawn or not to capture. But the cure is usually easy and permanent, once you realize what the trouble is. I have seen many MOS organs with this kind of tab switch where the central tongue gets covered over with some kind of black or gooey substance that seems to settle out of the air. Electrical conduction gets flaky, and problems develop. We clean them up with a Q-tip dipped in alcohol, then carefully bend them so that they make good contact when the tab is down but clear the tongue when it is up.
    John
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    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

    https://www.facebook.com/pages/Birds...97551893588434

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