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Thread: JC-120 from bad to worse

  1. #1
    Junior Member
    Join Date
    Mar 2009

    JC-120 from bad to worse

    So I recently bought a mid to late 80s JC-120 made in USA to replace the one I sold stupidly in 2001. Found it on Craigslist locally for $300. A bit unloved on the outside, but everything worked when I bought it. Volume pot was bent, so I tried bending it back gently. Broke. Took amp out to get part number for pot, and discovered 1/4" jacks were cracked and falling apart. After patching it, spraying contact cleaner on the pots, air dusting, and reassembling it, I tested it. Worked. Tested it later in the afternoon, and got silence. Then tried it again, and now only the right speaker works. No swooshy chorus. Did a fuse blow? Or is it time to give up and haul it in for repairs? I do basic soldering to replace pots/caps etc on vintage radios/phonos. But with my recent luck, I'm gun shy. Any advice/help?

  2. #2
    Old Timer
    Join Date
    Jun 2006
    Norristown state hospital
    If it ain't broke, don't fix it!
    besides the mains fuse, there are two smaller fuses for the + and - voltage supplies. They are probably fines since the amp powers up.
    The wires may be brittle from age, and you may have broke one or more while working on it.
    If one speaker works, check the wiring to the other.
    Try swapping the speaker wires around to see if the speaker is okay, or if one of the outputs is bad.
    check and clean the fx loop jacks, and all the output and switching jacks on the back panel.
    You may want to replace all the input jacks if they are falling apart.
    Write down where all the wires go, take your time, be careful and don't get frustrated.

    I worked on one last week that had a couple of intermittant connections and loose wires, but these things are built well and usually work pretty good with some maintenance and TLC.

  3. #3
    Senior Member
    Join Date
    Jul 2007
    I'm told that contact cleaner in a pot (especially a plastic-element one) is a great way to kill it (melt the element). No personal experience, but I did get smacked around for suggesting it once. There is a pot cleaner, but don't recall the name.

    Apart from the speaker swap - is there a loop? More than one? Stereo return?
    If you have a stereo loop return, you could try injecting signal there and see if the dead channel wakes up.

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