Jupiter 4 making sound but not well

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acidbrother
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Jupiter 4 making sound but not well

Post by acidbrother » Thu Nov 21, 2013 10:54 am

I got a jp4 a bit ago. doesn't work correctly. When I turn it on all it does is some odd arpeggiating. The keyboard and controls do nothing as far as I can tell. I am going to open it up soon. Any idea what this could be?

Thanks

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Re: Jupiter 4 making sound but not well

Post by nathanscribe » Thu Nov 21, 2013 11:49 am

Mine plays up in similar ways sometimes, haven't got round to properly troubleshooting it yet, but an initial peek suggested something to do with the mode selection buttons and the 5V (IIRC) logic around them. I know my own JP4 has other semi-dead logic inside, so that might be a start.

Sorry I can't be of more use.

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Re: Jupiter 4 making sound but not well

Post by Dr. Phibes » Fri Nov 22, 2013 3:51 am

One easy first step is to check that every connection inside is secure. May seem silly but I've had a couple of occasions when odd behaviour turned out to be the fault of an iffy molex connector.

If that doesn't solve anything it might be worth checking control board E (the arpeggio & key mode buttons on the bottom left) - it's just some manual switches and 3 switching diodes. Looks like if diode 3 failed it would cause a short between pins 1& 35 of the microprocessor which could cause a malfunction (according to the manual, the voltages across these are involved in key assignment and arpeggiator mode selection).

But as nathanscribe says this kind of problem is often the hallmark of a failing logic chip (I see a few 4000 series in the key assign board) which certainly isn't unusual in a synth of this age. Harder to pinpoint those.

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Re: Jupiter 4 making sound but not well

Post by acidbrother » Fri Nov 22, 2013 11:30 am

I will check those things out when I open it up. I will let you know what i figure out. Thanks!

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Re: Jupiter 4 making sound but not well

Post by Steve Jones » Fri Nov 22, 2013 1:17 pm

Look for cracks in the earth track running across the top panel board, they often break if there is a any impacts on the control surface.
Synthesizer service tech since 1982.
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Re: Jupiter 4 making sound but not well

Post by acidbrother » Tue Jan 28, 2014 5:29 am

still cannot figure it out probably going to take it to a guy someday.

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