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Allen 301C Polyphony issue

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  • Allen 301C Polyphony issue

    Hello All,

    I have an Allen 301C MOS1 organ in my parents' home. It has not been used for some time. It has worked well for many years, however when I turned it on today, it appears that only the celeste analog stops will play (and even at that, I am only getting sound from about 2/3s of the middle range of the manuals.) the "digital" voices will only play one note at a time, and when I try to hold a chord, I only get one note.

    Any idea what is going on? I've checked the amps, etc.. but cannot find anything out of the ordinary.

    Thanks for the help. This forum is great!

  • #2
    RE: the analog celeste. There are only 37 notes of that, so it does only play from tenor C up to the 2nd C above middle C. That's normal.

    The first thing that comes to mind with a dead or nearly-dead MOS system is that the pedals may not be properly seated and may be holding many notes "on" and thereby robbing all or nearly all the polyphony. You can try lifting the pedalboard and settling it back in place, or pulling the pedalboard completely away from the console and then see if the manual stops will play. If they do, you will have to carefully reseat and adjust the position of the pedalboard so that it doesn't lock any notes on.

    Troubleshooting always begins with power supplies, so you need to first ascertain that you are getting stable, clean, on-the-money output from the -27, +5, and -5 terminals of the MOS supply. Use a meter to measure from each terminal to ground.

    Note that the +12 is unregulated and can be about anywhere from 12 volts to 16 volts. It's mainly used for relays and isn't critical. But it does have to be there. If missing, check the fuses on the 12 volt supply chassis.

    Thorough maintenance is the next step. You can find discussions of that in various places on the forum. Basically, you need to carefully remove each board in the system, one at a time, taking static precautions, and give all the card-edge connectors a thin coat of Vaseline, wiping nearly all of it off before re-assembling. Do the same with all the RCA plugs/jacks, and with the fanning strips and screw terminals. Every spot in the organ where metal meets metal needs to be cleaned.

    Don't neglect the transposer switch. This big complicated rotary mechanism MUST make perfect contact in all 12 positions and must snap into a securely conducting position with each click.

    Once you've done all this, exercise the voltage regulating pots on the power supply and set the voltages dead-on with a meter.

    Look over every one of the push-on plugs bristling with wire-wrap terminals and make sure that none of the pins are bent and possibly touching another pin or something else. I have seen more than one MOS system dead because of that one thing.

    After all that, you might have it working. Turn on one stop at a time and try each one to see if it plays correctly. Make notes of any that do not. Stops that seem stubborn may simply need their stop switch cleaned with a Q-tip moistened in alcohol.

    Beyond all this, there is little that can be done other than having an Allen tech come out and swap out boards.
    John
    ----------
    *** 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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    • #3
      jbird, you are awesome! Turns out the pedalboard was the problem. Readjusted and no more polyphony problems. Now, on to cleaning up some stop contacts and giving the old girl a good overhaul!

      Many thanks!

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