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A very bothersome sporadic problem with Johannus AC-V in our church

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  • A very bothersome sporadic problem with Johannus AC-V in our church

    First, since this is my first post, I'll introduce myself. I'm a retired electrical engineer who worked in a lot of varied areas of technology during my career. I know just a little about digital organs, but without having block diagrams and schematics in front of me, the necessary test equipment, and knowledge of the processor(s) in our organ, it is just a big "black box."

    Our church acquired a Johannus American Classic V organ about 8 years ago. It's a three manual organ with (as I recall) 24 audio channels for the external speakers, with some of the channels driving an antiphonal section at the rear of the sanctuary. We've were quite satisfied with the instrument until some "glitches" started showing up about a year ago. Unfortunately, we learned that the dealer who sold us the organ had lost the dealership as a result of a Johannus business decision. The dealer also was an engineer and organist who provided us with maintenance as needed. We no longer have a organ maintenance specialist within a reasonable distance to depend on. We were, however, given the name of a person who is about 2.5 hours away, so we're looking at a substantial charge just because of the distance. We would be very happy to pay that driving fee plus other charges to troubleshoot and repair IF we could be certain they could isolate and provide a path to eliminate the problem.

    Here is a description of the problem, which I call a rogue state, lacking a better name:
    At random times, the organist will be playing or practicing, and the organ goes into a state where a loud raucous sound is suddenly played from the speakers. Depressing any key on any of the manuals results in this same sound, which is somewhere between a fagatto and a fog horn. The same sound is played, no matter which key is depressed, on any of the three manuals. Pressing the clear (O) button does nothing. Pushing or pulling a stop will not turn it on or off. The only way to clear this condition is to turn organ power off for a few seconds, then turn it back on and the organ is then to the normal startup condition.

    There is another "rogue state" that I've been able to experience myself a couple of times, once when I had just turned the organ on. No stops were indicated as on, but when I touched a key on the swell manual, a note played. I found I could play a full chromatic scale on that manual, but not on the choir or great. I depressed the clear button, but it didn't change anything. I also could not add a voice to the swell manual or to the choir or great manuals. Only turning power off and back on would reset the organ to a normal state.

    I know from my experience in other areas that this type of problem is the most difficult to pin down and fix. If anyone has experienced anything similar with a digital organ, I would appreciate your insight and advice.


  • #2
    A lot of Johannus organs from that time frame have problems with the connectors that carry power to the various boards from the power supply. these are usually yellow in color, and push down on some large pins that are soldered to the boards. These connectors over time become unreliable in their ability to provide the boards with enough current, and the organ becomes erratic in various ways.

    The official "cure" is to bypass the yellow plugs by soldering the power wires directly to the boards all over the organ. It is most critical in the tone generator section though, far less so in the amplifier and other analog parts.

    To be honest, in some organs I've been able to fix the problem by simply cleaning up the yellow plugs and the mating pins, and sometimes bending the spring-like mating parts inside the plugs so that they grip the pins more firmly.

    Whatever you do, be careful. I have seen more than one Johannus nearly ruined by an amateur fixer trying to reflow the solder on the boards, or trying to force molten solder down into the plugs.

    One other thing to check -- if the organ in question has a 5 volt switching power supply in a small rectangular metal cage, it may have become erratic in voltage. The cure is a new one, but the problem is merely that the adjusting potentiometer is dirty and makes intermittent contact at the wiper point.

    Good luck!
    *** 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!


    • #3
      As a former owner of an AC-V organ, we are very familier with their functions and behaviors. I'm sure we can help you if you're not too far away.
      Please send me a private message with your location, phone #, name, etc. Thank you.


      • #4
        Thanks John,

        I appreciate your suggestions. Although I've done my share of soldering of electronics in my life, I would prefer to get someone who is very familiar with this particular organ. You mentioned a 5 volt switching supply. I do know from some maintenance visits in recent years, I recall that a 5 volt supply was adjusted to be 5.1 or 5.2 v, as I recall. How many different power supplies are in this organ, and are they all switching supplies? Are the contact surfaces of the yellow plugs you mentioned gold plated?

        While I was trying to cause the organ go into one of the "rogue states" one day recently, and while I was playing scales, I heard the sanctuary air conditioner (AC) compressor kick on, and noticed that the organ briefly dimmed slightly. It didn't cause any issue, however, with the registration I was using. Would you have any concern that the starting surge of a very large AC could be involved? Since we had no problems for at least 5 years, I'm guess not.

        Thanks again, Glenn


        • #5
          Hi Gary,

          I sent you a PM with my location and contact info. Since you have experience with this AC-V, would appreciate 5 minutes or so of your time.


          • #6

            Sounds like it could be a bad contact somewhere.

            A couple of other things,

            1) does this organ have the tone generators and amps, in the console or are they external?
            2) if external, check, if you can, with a MIDI monitor to see if there is any unusual activity. JOHANNUS organs control system is done via MIDI.
            3) check the voltage output of the 5 volt supply. JOHANNUS recommends a reading of at least 5.1 volts.



            • #7
              All the electronics are internal to the console, and they are located on three slide-out shelves (I think it's three). As for the tone generators, it is my understanding that 24 bit digital recordings of individual pipes are accessed and played in a loop while a key is depressed to recreate the sound. My memory is that there are 24 separate audio channels. So for a modest registration, each voice (stop) could be played through a separate channel to avoid intermodulation distortion. One is for a very large sub-woofer, which does have it's own amplifier. Up to now, only technicians representing Johannus have touched the electronics since it has been in our church.