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favorite this post Re: Roland Jazz Chorus 120 easy fix? (Gainesville, FL) hide this posting unhide

make / manufacturer: Roland
model name / number: JC 120

Just so you prospective buyers will know, here's what that "easy fix" will require.
You will have to remove the whole chassis from the amp. Don't forget to disconnect the speakers and the reverb tank.
Discharge the power supply caps....you know how to do that without getting zapped....or worse, right?
You'll have to disconnect the circuit board from the power transistors....the 5 white molex connectors across the wiring harness. Be careful that you don't generate static electricity and zap the power transistors...or any solid state component in the amp. You do have an antistatic work station, right?
You might be able to get by without disconnecting the power supply board, but that means bending the wire harness without doing any damage. Otherwise the power supply board has to come out too.
You'll see that the broken volume pot is soldered through the circuit board....as are all the pots, switches, and jacks. That means you will have to remove all the knobs and nuts from the front panel....don't break any more of them, don't scratch the hell out of the faceplate....to get the circuit board out and turned over so you can unsolder the broken volume pot. You do know how to unsolder without damaging a circuit board, right?
Now, you were able to find the correct replacement volume pot somewhere, right? I just did a quick check with Roland parts online, no pots shown on their list of available parts. Also checked ebay, no pots available there either. How about Radio Shack....opps, they are gone! I did see a few knobs available, not sure if they match or not. I hope they are the correct shaft size for whatever pot you can find.
Now you can solder in the new pot you eventually found.
And reassemble all the stuff you had to undo to get this "simple fix" accomplished....in the correct order....without breaking anything else.
What could go wrong, huh?
Oh yeah, most decent technicians would have checked out the whole amp before starting this "simple fix" and checked the repair notes available for these amps. These amps are notorious for having noise as they get older, and sometimes the reverb is weak or just bad altogether. At the very least they will probably tell you that while you are in there, it would be a good idea to replace the filter caps now....otherwise it will be another whole disassembly job to get them when they do....kind of a pay me now, or pay me again later idea.

Now I'm not trying to pile on the seller here. After all, he did say there was a problem. You can just leave it as is and be happy. But as for a simple fix, well, that's not what I would call it as far as labor is concerned. And be sure you can get that volume pot....that fits the circuit board....before you start.

Oh, and I've included a photo of the inside of one that was in for a recap job to cut down the noise.
This is what you'll see when you first open it up.
But it should be simple, huh?
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