jp-8000 pot problem

Forum for JP-8000/8080 synthesizers from 1990's
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JonnyJFunk
Posts: 1
Joined: 02:24, 18 August 2010

jp-8000 pot problem

Post by JonnyJFunk »

Hey guys,

I have a very frustrating problem with my jp-8000.

I noticed one day that my range knob stop working. Since I never really used the knob I didn't put too much thought into it and just figured I'd fix it when I got around to it. the temp scope said that it was stuck at +110.

But now, I am completely unable to play the synth. After I select any preset the range knob will flutter between +110 and +112 and sometimes jump all the way to +wide, no matter where the knob actually is. I don't have to touch the knob, it will make this jump after I play a few keys

I've done a lot of experimenting, and here is what I know so far:

1. At first I was able to temporarily change the range by pressing the knob down a bit.

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If I turned the knob without any pressing the synth would not register the movement. This only worked a few times before it completely stopped. It reminded me of a pair of junky headphones. eventually the solder gets loose and you need to fidget with the chord to get the phones to work again, but eventually you need to open up the phones and re-solder.

2. The problem is completely isolated to the range knob.

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Aside from removing the key bed to regrease some keys I've never gone much deeper inside the synth. I thought the unresponsiveness might be wires needing to be resoldered(like a guitar pot) but I found out that this is not how the knobs work, they are directly attached the board. I decided I could only do more harm than good and quickly reassembled my synth.

3. The fluttering is encouraged by physical movement.

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If I hardly press a key the range scope may not jump. This is not always constant, as the knob will jump on its own as well. But when the synth is played it certainly expedites the process

Well, that's about all of the information I can think of right now. If anyone has any advice I'd really appreciate it. Through my experience it seems that when a computer board goes you need to replace the entire board. I really hope this isn't the case!
Senso
Posts: 2
Joined: 02:41, 31 August 2009
Location: Amsterdam
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Re: jp-8000 pot problem

Post by Senso »

My first reaction would be: replace the pot. :-)
But the fact that the problem gets worse when you play the synth, opens another possibility...
I would say first of all check the flat cable connectors of the board the pot is mounted on. Often dirt collects in there or the contacts start to oxidize. Pull them and re-seat them a couple of times. This usually is enough to reestablish a good contact.
When this does not help, replace the pot.

When both of these do not make the problem go away, it's time for Plan B:
Cry for help!

Good luck,
Senso
Electrowind51
Posts: 4
Joined: 20:08, 15 February 2011

Re: jp-8000 pot problem

Post by Electrowind51 »

I've had simalar problems. When I received my used unit it was defective. I do some of my own tech work, so I opened up the unit. What I found was that the pots are directly mounted on the circuit board ( typical for most modern stuff). Due to rough handling in shipment or prior, the soldering of several pots to the circuit board had come loose. All that I did was to resolder these connections (really just touch them up with some fresh solder). Problem solved, no other problems in the last seven years, even the display is as bright as ever.
KonaKurt
Posts: 13
Joined: 20:46, 26 August 2010

Re: jp-8000 pot problem

Post by KonaKurt »

Jonny. I must say that I have never had any problems with my JP so far...fingers crossed!
But if the temp scope always registers an extreme value for the range, as you describe, I would say it is either a loose connector needs resoldering someplace, or that the actual pot is fualty and needs replacing. If it was me, I would try replacing the pot first, and then if that did not work, keep the new pot as a spare anyway (you never know when you might need one) and prepare to do some resoldering. If in doubt, find a synth repair workshop/dealer who can do it for you, BUT always get a QUOTE or at least an estimate first, because sometimes synth repairs can be very expensive.

Kurt.
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