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My MG-1 is only heard by dogs and insects....

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  • Rob
    Hello group, I have an MG-1 that I purchased last year from an antique mall. I used a friend s when I was younger and loved it, so when I found this one (even
    Message 1 of 7 , Oct 16, 2007
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      Hello group,

      I have an MG-1 that I purchased last year from an antique
      mall. I used a friend's when I was younger and loved it, so when I
      found this one (even though it was defective) I had to have it. I
      figured at the least it was worth a try. I have researched these
      quite extensively and own both manuals. The problem I am
      experiencing does not apear to be listed on any boards or MG-1 sites
      that I know of. I have cleaned it up and very slowly removed the
      black goo from under the shell. I have checked solders and point to
      point checked everything I can think of w/ a volt-ohm meter although
      I am not too proficiant when it comes to testing ICs.
      I can only find one glaring symptom of it's disfunction. It
      only makes very high frequency tones. The keys all change the
      pitch. The sliders all modualate the sound. In fact, it sounds
      exactly like I remember my friend's sounding back in the day.
      Except the frequency is so high and faint if you didn't know what
      you were listening for you might not even notice it. Kind of like
      the sound when you leave the tv on with the volume turned all the
      way down, but you know the TV is still on because of that high
      pitched noise that only dogs should be able to hear? Same w/ some
      floresent lights. Anyway, I haven't wanted to start ripping a part
      my moog with out a second opinion or at least some advice.
      The conclusion I have half-way come to is #6 in the service
      manual. 6) Output is very low or intermittent Remedy/cause
      Defective VCA circuit U1011, Q1028.

      Which is IC CA3080AE made by RCA
      &
      Transistor 2N386 ? made by Motorola

      I'm new to the group and would love some advice. I've writen
      Chipforbrains on ebay to see about replacements and never got a
      reply. Maybe what he has on his auctions is all he has I don't
      know, but I am kind of attatched to the old MG-1 now and don't want
      to give up on her. Sorry this is such a long post, I haven't had
      anyone to talk to about my moog, they just wouldn't understand ; )

      Thank you very much,

      Rob
    • malcolm palin
      Are you hearing this high pitch output from the headphone and rca outputs? I usually just use the headphone output on the front because it s cleaner (mine is
      Message 2 of 7 , Oct 16, 2007
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        Are you hearing this high pitch output from the headphone and rca outputs? I
        usually just use the headphone output on the front because it's cleaner
        (mine is anyway).

        malcolm


        >From: "Rob" <goc_germs@...>
        >Reply-To: moogmg1@yahoogroups.com
        >To: moogmg1@yahoogroups.com
        >Subject: [moogmg1] My MG-1 is only heard by dogs and insects....
        >Date: Tue, 16 Oct 2007 19:41:35 -0000
        >
        >Hello group,
        >
        > I have an MG-1 that I purchased last year from an antique
        >mall. I used a friend's when I was younger and loved it, so when I
        >found this one (even though it was defective) I had to have it. I
        >figured at the least it was worth a try. I have researched these
        >quite extensively and own both manuals. The problem I am
        >experiencing does not apear to be listed on any boards or MG-1 sites
        >that I know of. I have cleaned it up and very slowly removed the
        >black goo from under the shell. I have checked solders and point to
        >point checked everything I can think of w/ a volt-ohm meter although
        >I am not too proficiant when it comes to testing ICs.
        > I can only find one glaring symptom of it's disfunction. It
        >only makes very high frequency tones. The keys all change the
        >pitch. The sliders all modualate the sound. In fact, it sounds
        >exactly like I remember my friend's sounding back in the day.
        >Except the frequency is so high and faint if you didn't know what
        >you were listening for you might not even notice it. Kind of like
        >the sound when you leave the tv on with the volume turned all the
        >way down, but you know the TV is still on because of that high
        >pitched noise that only dogs should be able to hear? Same w/ some
        >floresent lights. Anyway, I haven't wanted to start ripping a part
        >my moog with out a second opinion or at least some advice.
        > The conclusion I have half-way come to is #6 in the service
        >manual. 6) Output is very low or intermittent Remedy/cause
        >Defective VCA circuit U1011, Q1028.
        >
        > Which is IC CA3080AE made by RCA
        > &
        > Transistor 2N386 ? made by Motorola
        >
        >I'm new to the group and would love some advice. I've writen
        >Chipforbrains on ebay to see about replacements and never got a
        >reply. Maybe what he has on his auctions is all he has I don't
        >know, but I am kind of attatched to the old MG-1 now and don't want
        >to give up on her. Sorry this is such a long post, I haven't had
        >anyone to talk to about my moog, they just wouldn't understand ; )
        >
        >Thank you very much,
        >
        >Rob
        >
        >
        >
        >
        >Yahoo! Groups Links
        >
        >
        >
      • Rob
        Hey Malcolm, Thanks for responding to my post. Yes I hear it when I run it out through the RCAs and when I run a direct line out of the headphone jack. It s
        Message 3 of 7 , Oct 17, 2007
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          Hey Malcolm,

          Thanks for responding to my post.

          Yes I hear it when I run it out through the RCAs and when I run a
          direct line out of the headphone jack. It's as if there is just no
          amplification.
        • malcolm palin
          Hmm....sounds like a bad amp chip or a bad connection obviously in the audio path. You might need to get some electronics tech to take a look and especially
          Message 4 of 7 , Oct 18, 2007
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            Hmm....sounds like a bad amp chip or a bad connection obviously in the audio
            path. You might need to get some electronics tech to take a look and
            especially the IC's.


            >From: "Rob" <goc_germs@...>
            >Reply-To: moogmg1@yahoogroups.com
            >To: moogmg1@yahoogroups.com
            >Subject: [moogmg1] Re: My MG-1 is only heard by dogs and insects....
            >Date: Wed, 17 Oct 2007 23:00:03 -0000
            >
            >Hey Malcolm,
            >
            >Thanks for responding to my post.
            >
            > Yes I hear it when I run it out through the RCAs and when I run a
            >direct line out of the headphone jack. It's as if there is just no
            >amplification.
            >
            >
            >
            >
            >Yahoo! Groups Links
            >
            >
            >
          • Andreas Gregor
            Possibly a problem with the supply to the keyboard or perhaps in the signal path coming back from the keyboard CV to the oscillators. ... From:
            Message 5 of 7 , Oct 18, 2007
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              Possibly a problem with the supply to the keyboard or perhaps in the signal path coming back from the keyboard CV to the oscillators.
               
               
               
              -----Original Message-----
              From: moogmg1@yahoogroups.com [mailto:moogmg1@yahoogroups.com]On Behalf Of malcolm palin
              Sent: Thursday, October 18, 2007 4:08 PM
              To: moogmg1@yahoogroups.com
              Subject: RE: [moogmg1] Re: My MG-1 is only heard by dogs and insects....

              Hmm....sounds like a bad amp chip or a bad connection obviously in the audio
              path. You might need to get some electronics tech to take a look and
              especially the IC's.

              >From: "Rob" <goc_germs@yahoo. com>
              >Reply-To: moogmg1@yahoogroups .com
              >To: moogmg1@yahoogroups .com
              >Subject: [moogmg1] Re: My MG-1 is only heard by dogs and insects....
              >Date: Wed, 17 Oct 2007 23:00:03 -0000
              >
              >Hey Malcolm,
              >
              >Thanks for responding to my post.
              >
              > Yes I hear it when I run it out through the RCAs and when I run a
              >direct line out of the headphone jack. It's as if there is just no
              >amplification.
              >
              >
              >
              >
              >Yahoo! Groups Links
              >
              >
              >

            • Andreas Gregor
              If it is the 3080 you can still buy them from either www.mouser.com or www.newark.com. ... From: moogmg1@yahoogroups.com [mailto:moogmg1@yahoogroups.com]On
              Message 6 of 7 , Oct 18, 2007
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                If it is the 3080 you can still buy them from either www.mouser.com or www.newark.com.
                -----Original Message-----
                From: moogmg1@yahoogroups.com [mailto:moogmg1@yahoogroups.com]On Behalf Of Rob
                Sent: Tuesday, October 16, 2007 3:42 PM
                To: moogmg1@yahoogroups.com
                Subject: [moogmg1] My MG-1 is only heard by dogs and insects....

                Hello group,

                I have an MG-1 that I purchased last year from an antique
                mall. I used a friend's when I was younger and loved it, so when I
                found this one (even though it was defective) I had to have it. I
                figured at the least it was worth a try. I have researched these
                quite extensively and own both manuals. The problem I am
                experiencing does not apear to be listed on any boards or MG-1 sites
                that I know of. I have cleaned it up and very slowly removed the
                black goo from under the shell. I have checked solders and point to
                point checked everything I can think of w/ a volt-ohm meter although
                I am not too proficiant when it comes to testing ICs.
                I can only find one glaring symptom of it's disfunction. It
                only makes very high frequency tones. The keys all change the
                pitch. The sliders all modualate the sound. In fact, it sounds
                exactly like I remember my friend's sounding back in the day.
                Except the frequency is so high and faint if you didn't know what
                you were listening for you might not even notice it. Kind of like
                the sound when you leave the tv on with the volume turned all the
                way down, but you know the TV is still on because of that high
                pitched noise that only dogs should be able to hear? Same w/ some
                floresent lights. Anyway, I haven't wanted to start ripping a part
                my moog with out a second opinion or at least some advice.
                The conclusion I have half-way come to is #6 in the service
                manual. 6) Output is very low or intermittent Remedy/cause
                Defective VCA circuit U1011, Q1028.

                Which is IC CA3080AE made by RCA
                &
                Transistor 2N386 ? made by Motorola

                I'm new to the group and would love some advice. I've writen
                Chipforbrains on ebay to see about replacements and never got a
                reply. Maybe what he has on his auctions is all he has I don't
                know, but I am kind of attatched to the old MG-1 now and don't want
                to give up on her. Sorry this is such a long post, I haven't had
                anyone to talk to about my moog, they just wouldn't understand ; )

                Thank you very much,

                Rob

              • phillip m gallo
                Rob, Hard to diagnose with so little symptom description, but the description you give is intriguing. I understand it is very high pitched but otherwise
                Message 7 of 7 , Oct 22, 2007
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                  Rob,

                  Hard to diagnose with so little symptom description, but the
                  description you give is intriguing.

                  I understand it is very high pitched but otherwise functional. Lot's
                  of situations could cause this symptom.

                  The synth has VCO's, VCF's VCA.

                  Working backwards, does the VCA appear to work i.e. using the 3
                  positions of the "Keying" switch does it work as continuous, keyed and
                  enveloped. If it does, i'd look to the filter next.

                  With the VCO's "potted down - off", the filter at max resonance will
                  oscillate. Does it do this? Does it respond to filter frequency
                  settings? Does it responds to the envelope? If so the VCO's are
                  suspect.

                  With Resonance off, filter mid-position, listening to the VCO's one by
                  one do they respond to the 8ve switches? Do you hear diff waveforms
                  when you switch them?

                  If yes to the above the control voltage circuit could be the problem.

                  Please let us know what you find.

                  regards,
                  p


                  It could just be your filter frequency is need max (due to pot
                  characteristics) and while resonance is at max.
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