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Thread: Roland JC-120 BB03539

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    Roland JC-120 BB03539

    Jazz Chorus amp chorus and vibrato not working. I think this is the 1984 model. I have opened it up and am looking for help. Trying to figure out what is what and canít find a schematic. Any advice may help. Chorus and Vibrato might be very faint, not deep at all. It worked for years and years but would love to get it working again.

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    Senior Member nevetslab's Avatar
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    Theses are the two JC120 schematics I have. Usually will get you close even if they're not exact as being worked on.

    roland_jazz_chorus Schematic.pdf
    Roland-JC120-JC160 Schematic.pdf

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    I'm having the same problem. I took my JC 120 apart to clean the pots with deoxid and when I put it back together, the Chorus/Vib is no longer working. Anyone have a fix?

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    Senior Member nevetslab's Avatar
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    Welcome to the forum! On the Chorus PCB, depending on which schematic you have that matches your PCB, if you have a scope, see if you have the appropriate waveforms for the Chorus and Vibrato signals on that dual IC that supports the dual Chorus chip set. I often find that IC (IC 5 on one schematic, IC 8 on the other) has failed for some reason. Not unheard of for one of the Chorus chips to fail, but not usually. And, of course, check the work you did when you had the PCB out. I assume your comment 'I'm having the same problem' refers to you not having Chorus or Vibrato function on your amp.

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    Thumbs up JC120 Chorus Problem

    Quote Originally Posted by nevetslab View Post
    Welcome to the forum! On the Chorus PCB, depending on which schematic you have that matches your PCB, if you have a scope, see if you have the appropriate waveforms for the Chorus and Vibrato signals on that dual IC that supports the dual Chorus chip set. I often find that IC (IC 5 on one schematic, IC 8 on the other) has failed for some reason. Not unheard of for one of the Chorus chips to fail, but not usually. And, of course, check the work you did when you had the PCB out. I assume your comment 'I'm having the same problem' refers to you not having Chorus or Vibrato function on your amp.
    Thanks for replying! I was able to fix the problem. It was very odd. The treble pot would squeal if I turned it up more than halfway and the Chorus / Vib quit working. I found two wires that were hanging loose and was able to deduce where they were previously installed. After re-soldering them, everything works.

    I'm not an electronics person, but can solder if necessary. I'll have to replace some pots since the shaft has broken off of three of them. It looks like I'll have to remove the circuit board completely to do that. Saving that project for the future.

    Cheers
    Jilly

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