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Allen 505 B Percussion always "ON"

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  • Allen 505 B Percussion always "ON"

    How does one remove permanently the "percussion"? The percussion effect is slightly sounding on A computer but it's okay on the B computer. Disconnecting it at the stop tab doesn't cause the percussion to cease. The sustain control is "off" but it will increase the amount of sustain even when the percussion stop tap isn't "ON". Did replace the Keyboard Array board. Okay for a while then bad again.

  • #2
    According to the service manual, when you engaged the Percussion tab (in the swell only, right?), the tab causes two pins on J159 of both the A and B KBA boards to go to ground. These are pins 5 and 9, simultaneously turning on "sustain" and "piano mode" for both computer systems.

    If you are getting a percussion-like effect on one of the computers without having this tab on, either the KBA board is defective OR something else is shorting one of those pins to ground. You should find that pins 5 and 9 are tied together right at J159, and you should also find that the two pins of both KBA boards are connected to the same tab. (I can't remember if there is a diode on each leg or not. If so, it will be on the tone strip.) So somewhere along the way there could be a wiring fault.

    Check to make sure you don't have a bent-over wire-wrap pin on J159 of one or the other KBA. Trace the white wire on each one that leads back to the tab to see if there is a place where the insulation has rubbed off and the copper inside is touching some metal part of the organ. If there are diodes on the tone strip, check to see if one of them is defective.

    If none of this reveals anything, you can always disable the computers one at a time to determine which one is doing this, then swap the KBA boards from one to the other (with the organ powered off) and see if the problem moves with the board. If it does, then you have a defective KBA board. If it doesn't then you do have a wiring fault and you'll have to look harder!
    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
      Vrgrst,

      Could your computer possibly have Reverb attached to any of the manuals?

      Michael
      Way too many organs to list, but I do have 5 Allens:
      • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
      • Lowrey Heritage (DSO-1)
      • 11 Pump Organs, 1 Pipe Organ & 7 Pianos

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      • #4
        John,

        Thanks for the detailed response. I also received similar instructions from a Stan Harrison of Harrison Labs in Colorado. In my church organ, J 159 connects to the Stopboard array, not the KBA. The KBA is J 149 (at the top) and J 150 at the bottom. When I disconnect pin J 159 pins 5 & 9 , it disconnect two stop tabs on the Great manual. Stan Harrison said that on P151 pin 37 is the output signal so that should kill the sustain even if the board tries to generate the signal. However there is no wire connect to pin 37.

        Where is the "tone strip" located?

        The following was done but never completely solved the problem: April 2014 one of the KBA was replaced and April 2015 a MOS 2 Code was replaced. By switching the A & B MOS 2 Code, the problem still is "A". I haven't switch the KBAs. So it's okay to do that, they aren't identical? The "A" has the controls for the vibrato, sustain, motion.

        The percussion sustain effect is always sounding but hardly noticeable most of the time. After the organ has been on for 2+hours, the percussion effect sometimes becomes much more intense . Also the tremulant has become very "mild".

        I have taken pics of the boards which I could send to you.

        The organ service man just wants to put in new boards so I do truly appreciate your help!

        "A" KBA 904-5633 Ass'y - 081-6066 Sch "B" KBA 904-5661 Ass'y - 081 - 6075

        "A" SBA 2 904-5635 Ass'y (don't have Sch) "B" 904 - 5635 Sch. 081-6067 Sch

        Thanks, Vernon
        My email is [email protected]

        Stan Harrison's letter
        Hello Vernon,

        To be brief here are some ideas for you:

        1 "Percussion" is both the sustain P159 pin 9 and piano mode pin 5. Sustain is also on P151 pin 37.
        2 The celeste is on the TGU -2 (tone generator) J173 pin 41 and on the KBA called tempered tuning J150 pin 18.

        3. The sustain on the KBA is IC Z2051 which also generates the "reit" (re-iteration that you probably don't use). This is an MC556 dual oscilator IC and also involves POT R050 which should control the sustain time. IC Z024 MC4011 is the logic IC for the sustain and is probably the culprit?

        4. I would disconnect the pins in step 1 one at a time to see if this disables the sustain. I think P151 pin 37 is the output signal so that should kill the sustain even if the board tries to generate the signal.

        I hope this helps,

        Best regards,

        Stan

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        • #5
          The percussions remains "on" even with the reverbs units are not turned on or plugged in.

          Thanks, Michael

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          • #6
            OK. Definitive information! I just now perused all the MOS-2 info on the Allen tech site to be sure of what this is about. Some observations and a correction!

            (1) There IS a mis-print in the on-line service manual concerning the 505B. Stan Harrison was obviously looking at the same thing I was, and also gave you the wrong J-number due to the misprint.

            When I told you to look at J-159, that is what it says on the spec sheet for the 505. However that is WRONG! It is J-150 pins 5 & 9 that are grounded when the Percussion tab is turned on. J-150 is on the KBA board.

            So, scratch all that about J-159. It is J-150 that you should be looking at. I double-checked by viewing all the MOS-2 schematics, and in every one of them except the 505 the connector was correctly identified as J-150. It was only a mistake on the 505's docs.

            (2) I cannot find any explanation of why the KBA and SBA boards on your A & B computers don't look alike. According to the docs, they are supposed to be the same. Look at the numbers on the white tags. Both boards should be identified as "Keyboard Array" but if one of these is a revised version it might be KBA-2A or something like that. Anyway, they ARE interchangeable.

            So, check for any possible wiring problems on the one that seems to become percussive after warmup. If you don't find anything, try swapping the KBA boards between the A and B computers. If the problem moves to the other computer, then the board is obviously bad.

            There doesn't seem to be any documented way to turn off percussion on the board itself. The only thing that turns it on is the grounding of pins 5 & 9 on J-150. If it comes on by itself, then something is wrong with the board. There's always a chance you might find a spec of solder on a trace that is getting warm and then making contact with a neighboring trace. But BE CAREFUL not to damage the board. Allen will exchange it for a new one for a relatively small fee, but will charge a LOT if the board has been damaged by attempts to repair it.

            Let me know how it goes. Good luck!
            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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