Dead JX-3P - what to do?

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Dead JX-3P - what to do?

Postby ChefDeadpool » Sat Aug 15, 2009 9:03 pm

Okay, I have a completely dead JX-3P that was given to me by a friend. I'd like to get it going again. I opened it up and it has that burnt electronics smell, but I can't find anything damaged. Where do I start diagnosing this? I've never worked on a synthesizer before.

Thanks!
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Re: Dead JX-3P - what to do?

Postby HideawayStudio » Sat Aug 15, 2009 9:17 pm

ChefDeadpool wrote:Okay, I have a completely dead JX-3P that was given to me by a friend. I'd like to get it going again. I opened it up and it has that burnt electronics smell, but I can't find anything damaged. Where do I start diagnosing this? I've never worked on a synthesizer before.

Thanks!



Firstly - is it completely dead? ie. no LEDs no sound?
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Re: Dead JX-3P - what to do?

Postby rhino » Sun Aug 16, 2009 12:23 am

sometimes totaly dead ones are easy,,,sometimes not.
start with the basics:
fuse blown, new fuse blows too?
power socket and switch?
AC OUT of the xformer?
DC out of the rectifiers?
DC out of the regulators?

Loose or swapped connectors?
voltages on mainboard?
master clock running?

let us know

PS see post about SH-2000 for tech help.
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Re: Dead JX-3P - what to do?

Postby HideawayStudio » Sun Aug 16, 2009 2:51 pm

rhino wrote:sometimes totaly dead ones are easy,,,sometimes not.
start with the basics:
fuse blown, new fuse blows too?
power socket and switch?
AC OUT of the xformer?
DC out of the rectifiers?
DC out of the regulators?

Loose or swapped connectors?
voltages on mainboard?
master clock running?

let us know

PS see post about SH-2000 for tech help.


I seem to remember there are 3 fuses on the secondary side of the JX-3P PSU. It would be worth checking these first.
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Re: Dead JX-3P - what to do?

Postby Maschinengeist » Sun Aug 16, 2009 3:58 pm

I agree with rhino.

Do like the fruity loops bid and follow your nose. Usually, it's the transformer who's blowing up or something near, like the rectifier or even the filter capacitors.

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Re: Dead JX-3P - what to do?

Postby EmptySet » Thu Aug 20, 2009 12:28 pm

Not to hijack this thread, but I also have a dead JX3P. I know a few more specifics about mine though: something is wrong with the main board. The reason I know this is because I also have a working JX3P. I've swapped just this board and all is well when a known good board is installed. When the bad board is installed, however, the lights display at weird times (and wrong locations), the interface acts wonky when you press buttons. And it doesn't appear to make much (any?) sound.

So, my question is, how could I best go about diagnosing the problem with the bad board? I'm probably in a bit of a unique position in that I have a working JX3P that I can set up right next to the one with the bad board. Maybe I can compare various voltages, etc… between the two? I'm not scared of a soldering iron nor of VOMs. But that's about where my electro knowledge takes a dive. (I don't have a scope, for example) Any pointers?
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Re: Dead JX-3P - what to do?

Postby ChefDeadpool » Tue Feb 20, 2018 5:26 pm

So, this is my own old thread, I know, but I've come back to trying to repair this thing. It turns out it's not /actually/ dead. It's got an issue where it's fine for awhile, then just shuts off, sometimes it's when a key is pressed, or some other operation.

I've gained considerable skills in the intervening years with regard to electronics. Has anyone seen this behavior before? I'm considering changing out all the capacitors, as that seems to be the de-facto fix for dealing with old electronics these days.

When it's on, it works fine and has no issues.

Your thoughts?
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Re: Dead JX-3P - what to do?

Postby Rasputin » Tue Feb 20, 2018 6:42 pm

ChefDeadpool wrote:It's got an issue where it's fine for awhile, then just shuts off, sometimes it's when a key is pressed, or some other operation.

When it's on, it works fine and has no issues.


Those two statements are somewhat contradictory. Do you mean that once it powers on it will stay powered on until it is interacted with physically?

I would personally suspect that it's a board flex issue because if it was CPU/RAM/EPROM type of logic problem causing it to crash then it would probably always power on, but be prone to crashing during operation. Therefore, if it's crashing when a button is pressed then I'd suspect that it's board flex related because of the physicality of it, and not because the CPU hangs, etc.

Still, I'd check the PSU for proper voltage and make sure there's minimal ripple because I've seen crazy things happen with bad power. Make sure you're not chasing your tail by making sure the PSU is 100% before running yourself in circles with investigating other stuff. Bad power can masquerade as pretty much any weird symptom you can come up with -- you just never know.
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