Forum Top Banner Ad

Collapse

Ebay Classic organs

Collapse

Announcement

Collapse
No announcement yet.

Help needeed on Allen MADC-2110

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Help needeed on Allen MADC-2110

    HELP !

    I just lost all the voices on TG-2, channel 2 EXCEPT for the Violas II. The remaining channel 2 voices are sounding, but at very low volume - basically unusable. Channel 3 voices are working as they should.

    Any ideas ?

    Jim
    Last edited by jepsound; 09-24-2015, 02:08 PM.
    -----------------------------------------------------------------------------------------------------------
    Keeping (too many) old organs alive.
    Allen ADC 2110-T, Rodgers Trio 321B
    Conn 651, 713
    Hammond M-3 w/Leslie 120
    Hammond Solovox
    Mass-Rowe model 96 Carillon

  • #2
    The "G" pot on that channel is probably at fault. Use a miniature screwdriver to "exercise" the pot a bit by turning it back and forth gently through its range of motion several times. Then set it back to about where it was. That will probably do the trick. While you're at it, do the same thing with all the pots, BTMG, on all four channels (or all six, if you have the optional card reader).

    The reason you still hear the violas is that they actually come from both channels 2 and 3, not just 2, so you are hearing the part that comes from the other channel.

    If the "G" pot is not at fault, it could be the RCA plug and jack where the signal exits the cage, or another one of the RCA plugs or jacks in the signal path between the cage and the amp. As always, I recommend pulling each RCA connector loose, rubbing a bit of Vaseline on to both the pin and the shoulder, wipe most of it off, then re-insert firmly and gently.

    About the only other thing it could be is some kind of component failure, like a chip on the generator board or on the MADC Mixer, or in the Trem III if yours has them. But that is highly unlikely. I'm betting on the pot.
    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

    Comment


    • #3
      Not sure I completely understand the problem, but if it is an entire channel missing or muddied, you could have an intermittent problem with the amp. I have had two of these amps develop a similar problem. You can switch the offending channel's RCA input jack on the amp with that of another. If the channels return and those of another channel disappear, then your problem is that fifty pound boat anchor.

      Comment


      • #4
        John - You probably nailed it. Knowing there are multiple sources for the Violas helps. I will open the cage tomorrow AM and give those pots some gentle exercise. I did not want to mess with them today for fear of losing the Violas.

        Searchingferu - The amp was one on my first suspicions, however, I have gone thru the entire audio chain on all channels and all is good there.

        Thank you both !

        Jim
        -----------------------------------------------------------------------------------------------------------
        Keeping (too many) old organs alive.
        Allen ADC 2110-T, Rodgers Trio 321B
        Conn 651, 713
        Hammond M-3 w/Leslie 120
        Hammond Solovox
        Mass-Rowe model 96 Carillon

        Comment


        • #5
          Per advice from Jbird, I rotated the pots and heard no improvement. Just for kicks, I checked the volume levels with the TG-2 gain pot full CW and full CCW. No difference. Could the gain pot be defective?

          I have fairly good soldering skills. Is it advisable to try to change out this pot, if defective, or will it open another can of worms if I mess with this TG board?

          Jim
          -----------------------------------------------------------------------------------------------------------
          Keeping (too many) old organs alive.
          Allen ADC 2110-T, Rodgers Trio 321B
          Conn 651, 713
          Hammond M-3 w/Leslie 120
          Hammond Solovox
          Mass-Rowe model 96 Carillon

          Comment


          • #6
            I've never tried soldering on new pots, though I think it's been done. But pots don't normally fail completely like that, just get dead spots. May not be your problem after all. Before you do anything else, one more bit of routine maintenance might help. Very gently pry out the EPROMs on the board that holds channel 2, taking careful note of which EPROM goes in which socket, and noting the orientation of the "notch" in the end of each chip so you won't put on in backwards. Wipe the legs with a Q-tip holding a bit of Vaseline, wiping off nearly all of it. Then carefully re-insert, making sure the legs don't get bent or curled under. You might have to bend the legs inward just a tad to make insertion easier.

            I don't know that this procedure will fix it, but it's worth a try. You never know just where on that board a little discontinuity has developed, and the EPROM socket is always a suspect.

            Have you tried reversing the RCA plugs where the audio exits the cage on jacks #2 and #3? Doing so will tell you for sure if the problem is in the cage or not. When you swap those two plugs, if the voices of channel two are now working (though through the wrong amp and speaker), you will know that the cage is OK. But if they are still dead, your problem must be within the cage.

            If the problem proves to be outside the cage, you can follow the audio from the cage to the trem generators (if present), and any mixers or other boards on the way to the amps. Let me know what you discover.
            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

            Comment


            • #7
              Thanks, John..

              Switching 3 and 2 at the Cage cannot be done easily since the cables are just too short. However, I did use a Y adapter and split the ch 3 output of the USEM-1 to send both the Ch 2 and Ch 3 audio into the rest of the audio chain and I can get all voices. So I guess the TG-2 is OK and, like many have suggested, the real issue is somewhere in the audio chain. Thought I had done a thorough job on that but not so.

              This should be much easier to fix.

              Jim

              PS - Does anyone have a schematic of the Allen USEM-1 board. It is my prime suspect now.
              -----------------------------------------------------------------------------------------------------------
              Keeping (too many) old organs alive.
              Allen ADC 2110-T, Rodgers Trio 321B
              Conn 651, 713
              Hammond M-3 w/Leslie 120
              Hammond Solovox
              Mass-Rowe model 96 Carillon

              Comment


              • #8
                I can't find an actual schematic of the USEM-1 on the Allen tech site, but the flow chart shows that inputs numbered 370, 371, and 372 all get mixed together and outputted on 378. Likewise, inputs numbered 373, 374, and 375 get blended together and outputted on 380. That means there may be some spare inputs on the USEM-1 that you could try, just on the chance that the particular input where channel 2 is connected has a bad component. Try this:

                If channel 2 from the cage is currently going into jack #370, try moving it to #371 or #372, if either of them is unused in your configuration. Now see if the missing voices are playing. If so, you are home free. If not, read further:

                THIS IS IMPORTANT: If your organ is equipped with TWO of the "MADC AP-1" boards there is a little-known hidden feature that makes it possible to completely do without the USEM-1 in the circuit. So, if the little fix I just described doesn't do the trick, let me know and I will tell you what to do to make it all work without having to repair anything.

                Also, does your organ have a card reader? If not, it is even easier to totally bypass the USEM-1.
                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

                Comment


                • #9
                  John,

                  Moving the plug to #371 or #372 did not help.

                  I do have the card reader.

                  Please let me know the next step.

                  Jim
                  -----------------------------------------------------------------------------------------------------------
                  Keeping (too many) old organs alive.
                  Allen ADC 2110-T, Rodgers Trio 321B
                  Conn 651, 713
                  Hammond M-3 w/Leslie 120
                  Hammond Solovox
                  Mass-Rowe model 96 Carillon

                  Comment


                  • #10
                    Hmmm... Well that still doesn't prove beyond a shadow of a doubt that the USEM is the problem. Try one more simple thing and this will let me know for sure. Start by restoring all the RCA plugs to the jacks where they were originally, before your problem occurred. Now we know that there is a good signal coming out of the cage on all six channels, so we must determine where it gets lost.

                    On the MADC AP-1 board that serves the SWELL channels, you will notice that there is a cable plugged into J345, and that cable probably has tape around it marked "2-A" or possibly "2-5-A." You will have to undo some of the cable ties to do this, so do whatever it takes to loosen up that one cable so you can plug it in elsewhere.

                    Now, once you have that RCA plug free to move around, what you really should do first is discover what exactly it is carrying. Here's how to do that:

                    Since we know that channel 3 works perfectly all the way to the amp, we're going to try sending this 2-A or 2-5-A signal into the audio path where 3A or 3-6-A is now going. So, look on the same MADC AP-1 board, and see that in J348 you have a cable that is marked with tape as "3A" or "3-6-A". Remove that plug from the jack, and plug in the 2A or 2-5-A cable to J348.

                    Now test your organ and see if the stops that belong in channel 2 are now OK. If they are, then that proves they are making it through the USEM-2 and it is NOT the problem.

                    But, if the channel 2 voices are still absent after you move this cable, that will prove that the trouble is the USEM-1 and we can go on to making the minor wiring changes that will eliminate it from the circuit.

                    Let me know what you find out. The rest of the process is going to take me quite a bit of time to describe, so I don't want to do it unless I know for sure that the USEM is the bad board.

                    (Sneak peek: Let me only say at this point that your AP-1 boards already contain all the mixer circuitry that is needed on this organ. I really don't know why in the world Allen chose to insert that USEM-1 into the circuit, when all they had to do was bring all the channels together using the mixer functions built into the AP-1. If you want to make a guess as to what I'm going to tell you to do, just start by knowing that the presently unused inputs on the AP-1 marked "rhythm left" and "rhythm right" are mixed into the other two channels and express right along with them, eliminating the need for an external mixer. I've often used that little extra feature to mix the output of a MIDI box into the audio system on one of these organs.)

                    OK. Let me know what you find out with the test above and I'll give you the details on cutting out the USEM. Sadly, if the USEM is not the problem, we will have to zero in on the AP-1 and/or the USRM.
                    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

                    Comment


                    • #11
                      At Last !!!

                      It works !!

                      I determined the fault was in the cable between the USEM-1 J378 and the SW AP-1 J345. Replacing this cable with a new RCA-to-RCA cable made everything work OK again.

                      John - Thanks so very much for helping me navigate thru this problem. The Forum and it's members are such a great resource.

                      Jim
                      -----------------------------------------------------------------------------------------------------------
                      Keeping (too many) old organs alive.
                      Allen ADC 2110-T, Rodgers Trio 321B
                      Conn 651, 713
                      Hammond M-3 w/Leslie 120
                      Hammond Solovox
                      Mass-Rowe model 96 Carillon

                      Comment


                      • #12
                        That's wonderful! Nice bit of troubleshooting.

                        What you did is what any tech would do in the same situation. Use a known-good audio system and check the source, then follow the audio and discover where it's being lost. You did well.

                        Keep up the good work!
                        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

                        Comment

                        Working...
                        X