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JC120/160 effect board issues

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  • JC120/160 effect board issues

    Howdy all, name's Six. First time poster, long time lurker. In between customer repairs I've been working on my own project, a 1979ish JC160 I picked up in a poor state. I've managed to solve a few of the issues including a rebuild of the power supply, repairing the reverb and getting the modulation to work more than it was previously.

    Thankfully I have a copy of the correct schematics and service manual but I'm at a bit of an impasse with the Chorus/vibrato.

    I replaced the CMOS chips (4011 and 4013) as I wasn't getting a clock signal. Now I've got a clock and the cjorus and vibrato work somewhat. The voltages and frequencies are wrong however with basically all the waveforms. My clock is running near 330KHz and the voltage swings for the various waves and LFOs are very low. The moment the chorus or vibrato is activated it comes on but there's about a 4-5dB drop in volume and a very noticeable 'whooshing' sound. The vibrato is there but it's not as potent as it should be. The Chorus is weak and hardly audible.

    Anyone who's had similar issues and resolved them or if anyone has any recommendations as to what to check out first I'd be greatly appreciative.

  • #2
    Hi, good form would be to post or link a schematic, otherwise I have no circuit to refer to.
    Last edited by Enzo; 04-29-2017, 10:05 PM.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      https://drive.google.com/open?id=0B-...2k5bjhPLUxuOXc

      There we go. My serial is high 500000s so it's the last schematic in the book.

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      • #4
        Are the 15v rails correct?

        I'd be wanting to get that clock frequency right and check the components around the 4011.

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        • #5
          Rails were the first thing I dealt with. Rebuilt the whole supply as a cap was leaky and the 242 was shorted.

          I spent some more time working on it and the Chorus LFO is also no go. Half tempted to pull the board Or and just replace all the components, probably take me less time that trouble shooting. XD

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