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Rodgers 740 low volume

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  • #16
    Unfortunately, just one expression pedal.

    Looks like the other two channels work swell though! Thanks a lot for the help so far. I can't believe this thing is actually working now and I can play it. Even without that channel, things are still sounding pretty full. I do wonder though if the volume could be fuller with that channel that's missing
    Last edited by Esteban Enrique; 06-29-2020, 01:57 PM.

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    • #17
      toodles - as a recap:

      1. Audio has been raised to good level for the channels that work (2 and pedal)
      2. Subwoofer will be refoamed (surround on its way here)
      3. Channel 1 is way too quiet

      For the channel sound problem, I've checked to make sure that neither the speakers nor the cables are the problem. So this leaves the internals to check. Expression pedal seems to decrease the volume in this channel (from almost nothing to absolutely almost nothing), almost as if decrescendo-ing, and I am able to increase the volume through the preamp, but it barely does anything meaningful. I'm wondering what else to check. Some thoughts are:
      • Expression pedal lamps or cables
      • Power amp
      • Power supply
      • All other circuits (capacitors et cetera)
      I just don't know what to really 'check' with these things. Other than playing around with pots, I don't have more experience with circuits. I have a basic multimeter that I can use for testing things out, but as I said before I am not expert at these things but still, a quick learner (especially with the internet!). Interestingly, without this channel, I still get good organ sound through my two speakers (putting the base cable through one of the two full ranges). I'm sure, though, that I'm missing out on that other channel which doesn't really work right now.

      Organ power is not picking up the phone, by the way, so it looks like I am on my own with the help of this great forum!

      Peace

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      • #18
        Esteban,

        Disconnect the woofer until the surround has been replaced. You can damage the drivers if you use it with the surround missing.

        Myorgan's comments regarding the expression pedal lamp don't apply to this series of Rodgers organs--his info is for Allen organs. Rodgers handles the expression differently. I will check my manual on this organ to see if might be something in the expression circuit. (FYI, Rodgers uses a potentiometer for expression--the position of the potentiometer is encoded as digital information, and then that digital information is decoded to drive a lamp, which lights light dependent resistors to achieve the expression. That lamp is on the output preamp board under a black rubber cylindrical cover (about 2 inches in diameter).

        I'll post more after reviewing the circuit.

        Comment


        • Esteban Enrique
          Esteban Enrique commented
          Editing a comment
          Thank you, you are a God send! I will be eagerly waiting for the information. Given some basic instructions, I'm happy to fix these things. It's just so hard to find info online.

          I actually found that lamp with the cap and took a look at it but didn't think much of it so couldn't tell you what I found. But at least I know where it is, I'll look at it again tomorrow
          Last edited by Esteban Enrique; 06-29-2020, 03:19 PM. Reason: Added stuff

        • myorgan
          myorgan commented
          Editing a comment
          Esteban,

          Originally posted by toodles
          Myorgan's comments regarding the expression pedal lamp don't apply to this series of Rodgers organs--his info is for Allen organs. Rodgers handles the expression differently.
          Didn't I tell you I'd reached the end of my expertise due to my ignorance of Rodgers organs?!!! See, I'm learning along with you. Thanks so much for bringing up the issues on the Forum and being a part of it!

          Michael

      • #19
        Here's a quick test: try the organ with headphones. The jack is located on the underside of the key desk, near the knee panel--it's by the reverb level control. When you connect headphones, the speakers turn off. By listening through the headphones you can tell if both channels are working up to the amplifiers. The headphones have their own small amp. If you get both channels through the headphones, then the problem is between the input to the amp channel and the speaker--it could be that that amplifier channel is blown.

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        • Esteban Enrique
          Esteban Enrique commented
          Editing a comment
          Will do first thing tomorrow morning, unfortunately im not at the church right now. I spotted the jack before but had never tried it. How do I know if both channels are playing? All of the stops pretty much play through the channel that does work...

      • #20
        MIchael: there's no lamp in the pedal on a Rodgers organ, and no black dot. You're thinking of Allen organs. Rodgers organs use a pot on the expression shoe. The lamp used is on the preamp board, and the same lamp lights both channels simultaneously.

        Esteban:

        Use the headphones to test the channels into and out of the preamp. If both are working, then the problem has to be one of the following:

        1. A bad speaker.
        2. Bad speaker wiring.
        3. Bad connector panel in the organ where the speakers attach.
        4. Bad output connector on one amplifier channel.
        5. Bad amplifier channel.
        6. Bad input connector to the amplifier channel.
        7. There is a mute function on the preamp to silence the amps when an antiphonal speaker system is used alone or when headphones are used. All 3 channels use the same mute signal, but each channel has its own mute device (a FET, field effect transistor). If the FET is shorted, the channel won't produce any significant signal, though some bleed through and noise might be heard.

        Any of the issues 3 through 6 might be caused by a cracked circuit board in addition to electronic failure.

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        • Esteban Enrique
          Esteban Enrique commented
          Editing a comment
          I will check this today, if I can find a 1/4 inch headphone adapter, spent an hour looking for mine and couldn't find it! Hopefully something shows up at the church. I'll keep you posted

      • #21
        IMPORTANT UPDATE:

        Headphones reflect the external reality. In other words, left audio of the headphones is heard loud and clear, right side very very quiet. So now I wonder what the next step is?

        ​​​​The problem might be in the preamp? Not sure where to go next.

        Comment


        • myorgan
          myorgan commented
          Editing a comment
          Just to be sure, was the headphone jack plugged in completely, and was the 1/4" adaptor you found TRS (stereo) instead of TS (mono)? I'm just posting this to be sure nothing has been left to chance.

          Michael

      • #22
        myorgan yes plugged in all the way. It is TRS stereo. I tested it at home on my Roland piano, sounded good

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        • #23
          If the headphones confirm the problem, then probably one of the preamp op amp circuits has failed, or the settings for that channel are set too low. It may be time for a technician if adjusting the posts produces no improvement.

          Comment


          • Esteban Enrique
            Esteban Enrique commented
            Editing a comment
            I will play around a bit more with the settings, but unfortunately Organpower is not picking up the phone at all. I've called a bunch of times. I will have the either wait some time or try to learn some more so I can troubleshoot. Would schematics or other such manuals help with this?

        • #24
          Ok, so tomorrow I will take a second look at the preamp board and try to see if this solves my problem. I will also take a gander at the power amp to see if any adjustments can be made there.

          In terms of failed circuits, is there a guide on how to check this? Can I just replace capacitors in suspected trouble spots?

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          • #25
            There is an online form for service at Organ Power--I'd try that: http://www.organpower.com/contact

            There is no guide for failed circuits--you have to understand the electronic circuits and diagnose the problem from the schematic diagram by process of elimination.

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            • Esteban Enrique
              Esteban Enrique commented
              Editing a comment
              I filled out this form about a week ago, but no response. I think they are either out of business (due to Covid), very seldom by their phones or emails, and don't check voicemail. I hope I'm wrong and they call me back soon!

            • myorgan
              myorgan commented
              Editing a comment
              That's unfortunate, Esteban. We have another member who has had similar issues with his organ service company not responding. I guess these times have made it difficult on everyone.

              Have you tried nearby areas (i.e. Portsmouth, Worcester, New Haven, Providence, Portland)? Perhaps you can find someone there.

              Michael

          • #26
            Does the 740 use the same oscillators to produce the audio for both channels? If so, that would mean that the audio source is fine.

            Esteban has eliminated the rest of the audio chain after the amplifiers. So that leaves the amps and any audio modification circuits between the oscillators and the amps.

            Toodles, is it possible to test the signals going into the amplifiers (or other components) with something like a guitar amp or mixer board? What is the likelihood that the light dependent resistor for the channel 1 is bad? If it were bad would the channel be at full volume or quiet? Also, is it possible that for some reason the signal for channel 1 is getting blocked but the reverb through channel 1 is getting passed through (the very quiet sounds)?
            Last edited by samibe; 07-01-2020, 02:05 PM.
            Sam
            Home: Allen ADC-4500 Church: Allen MDS-5
            Files: Allen Tone Card (TC) Database, TC Info, TC Converter, TC Mixer, ADC TC SF2, and MOS TC SF2, ADC TC Cad/Rvt, MOS TC Cad/Rvt, Organ Database, Music Library, etc. PM for unlinked files.

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            • Esteban Enrique
              Esteban Enrique commented
              Editing a comment
              I can't answer your questions as I am totally inept with these things, but what I can say is that I can hear about the same sounds in both channels. The channel that works plays every sound, albeit playing the swell manual a bit quieter. The broken channel is simply very quiet yet still sounding. I feel like I should make a video going through the different conditions to show the symptoms better

          • #27
            Quick update:

            This is a little digression but here it goes:

            Went to go play today, and now the music stand and pedal board lights don't work! We moved the organ a few feet yesterday but i didn't think that would happen. The only thing I can think of is that there is some connection problems at the power source, as the light cables all look well attached at the lights and go straight to the power supply. Frustrating! I wonder now if this is related to the bigger problem ...

            Second, as I commented above, the channel that does work seems to transmit all the stops perfectly, despite the diagram noting a distinction in voicing between the channels. It's almost as if the channel that works is self sufficient. The swell manual, however, is quieter than the great, slightly so.. I wonder if the channels are divided by manuals? But it's not clean cut bc again the channel that works is giving me the whole shebang for sound (or at least from what I hear).

            Comment


            • #28
              Esteban--it sound like you may have some connection problems with the power supply to various circuits. Also, the power problems might be a fuse.

              The voices for this organ are roughly as follows: Channel 1 handles flute 2, reeds, harp, and string celeste; Channel 2 handles the principal & flute 1; in addition both channels carry bypass signal from the other channel; the by pass is used for chorus effect. Depending upon adjustment, you might very well hear most of the organ through a single channel.

              For a direct contact to organ power, try emailing "david*organpower" replacing * with @ and use dot.com as the domain.
              Last edited by toodles; 07-01-2020, 05:52 PM.

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              • Esteban Enrique
                Esteban Enrique commented
                Editing a comment
                Thanks for the email information, just shot him an email.

                Would checking fuses be worth it? I have a multimeter, just haven't used it much.

            • #29
              Checking fuses might get your lights back on, but it probably won't help with the dead channel, since it uses the same voltages that the good channel uses. Pull off the rubber cover on the preamp board--the expression lamp and photocells (light dependant resistors) are under it. (It is just a friction fit.) If one of the photocells is shorted, volume on that channel would be extremely low. If it is open, you'd have full volume.

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              • Esteban Enrique
                Esteban Enrique commented
                Editing a comment
                Great, I will take a look tomorrow morning. Thanks so much ! Ill update

            • #30
              Sounds to me like one of the OP-AMP chips has a dead channel. Try swapping U15 and U16 (they are socketed 8-pin DIPs) and see if anything changes. These are common inexpensive ICs and they do fail sometimes.

              I don't have my fold-out binder at home, just looking at the cramped PDF schematic, but I believe U15 is the last OP-AMP in the channel 1 chain.
              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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              • Esteban Enrique
                Esteban Enrique commented
                Editing a comment
                John

                Blessed to have your input, I will try this out today. I would ask for the schematic pdf, but I fear I'd have no use for it because of my lack of experience with circuits.

                EDIT: where do I find the OP AMP?
                Last edited by Esteban Enrique; 07-02-2020, 07:18 AM. Reason: Question
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