JX-3P saw volume / panel / bender issues

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DesolationBlvd
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JX-3P saw volume / panel / bender issues

Post by DesolationBlvd » Sun Mar 29, 2015 2:12 am

Foolishly, I'm taking on another project...

A JX-3P, advertised as "doesn't power on", pretty cheap. What I found out is that it means "doesn't boot up".

LFO trigger lights up when pressed, volume and brilliance seem to work (or at least the quiet background noise gets brighter and darker and quieter and louder), battery's good...

Replaced the bridge rectifier with a possibly wrong value - which fixed the +5V line. +15V, -15V, and +5V are now good.

+7V line now reads around +10V.

EDIT 4/5/15: Funny thing - it came to life, but not without issues:

- The saw is much quieter than the other waveforms
- The edit slider and write buttons don't work
- The bender doesn't work, it's bottomed out and jumps when I bend up. When I press the LFO trigger, it jumps and only drops back down when I bend down.

Probably a very screwy front panel board's at fault here for all but the first one...

EDIT 4/9/15: Write buttons are my fault, I should have known to switch it to "programmer" to write. Also found out that the S/H circuit might be at fault, the saw is close to full volume in the high octaves.

The +7V line, in the PG-200, seems to go through a voltage regulator anyway, so it should be okay...
Last edited by DesolationBlvd on Fri Apr 10, 2015 1:24 am, edited 7 times in total.
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Re: JX-3P doesn't boot up

Post by Dr. Phibes » Sun Mar 29, 2015 3:37 am

In the manual it shows a few ways to check if the CPU, RAM and clock are functioning properly on power-up with an oscilloscope. Worth a try. Before that though check all the connectors. I had similar problem once and it was due to a faulty connection to the mother board.

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Re: JX-3P doesn't boot up

Post by DesolationBlvd » Sun Mar 29, 2015 6:13 am

All the connections seem to be sound.

I have an oscilloscope, but it's at my workplace...Good thing they gave everyone a key.
Last edited by DesolationBlvd on Sun Mar 29, 2015 5:36 pm, edited 2 times in total.
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Re: JX-3P doesn't boot up

Post by madtheory » Sun Mar 29, 2015 3:59 pm

Doesn't look like it's a boot up problem. Looks more like an audio output problem. Get service manual, etc.

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Re: JX-3P doesn't boot up

Post by DesolationBlvd » Sun Mar 29, 2015 6:14 pm

madtheory wrote:Doesn't look like it's a boot up problem. Looks more like an audio output problem. Get service manual, etc.
Forgot to mention - all of the front panel buttons, except for LFO Trigger, are non-responsive. Doesn't receive or transmit MIDI.

On the oscilloscope, no response from pin 30 or 9 on the CPU. +5V rail was no good after all. Updated original post.


+5V reads +0.5V.
+7V (MIDI board) reads +4.17V

D4 + terminal: +4.17V
D4 - terminal: 0V
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Re: JX-3P doesn't boot up / power supply issues?

Post by Dr. Phibes » Sun Mar 29, 2015 6:46 pm

Yeah it's a PSU issue then; all the digital stuff is entirely reliant on the 5V supply. The 5V & 7V supplies are separate from the +/15V supply and just uses a standard 7805 voltage regulator. Replace that and I reckon you''l be good.

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Re: JX-3P doesn't boot up / power supply issues?

Post by DesolationBlvd » Sun Mar 29, 2015 9:31 pm

Dr. Phibes wrote:Yeah it's a PSU issue then; all the digital stuff is entirely reliant on the 5V supply. The 5V & 7V supplies are separate from the +/15V supply and just uses a standard 7805 voltage regulator. Replace that and I reckon you''l be good.
Just placed an order on Amazon for the 7805...Sucks that Radio Shack is gone and that I have to wait for it to arrive. :x
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Re: JX-3P doesn't boot up / power supply issues?

Post by rhino » Mon Mar 30, 2015 2:31 am

If that fixes it, great.

Next, check the circuit board behind the panel (has the buttons, knobs and sliders on it) for cracks in the traces at the corners near the holes for the screws that hold the board to the panel. Likely there are several traces broken.
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Re: JX-3P doesn't boot up / power supply issues?

Post by DesolationBlvd » Tue Mar 31, 2015 11:30 pm

Replaced the 7805, no dice. The voltages are still too low.

+5V reads +0.5V
+7V reads +3.1V

The voltages going in seem to be out of line. From left to right starting with orange and ending in black:

5.67 V (orange)
4.70 V (orange)
16.80 V (red)
16.80 V (red)
0 V (black)

The manual says the orange lines should be 9V?

Next step: The W02 bridge rectifiers?
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Re: JX-3P doesn't boot up / power supply issues?

Post by Dr. Phibes » Wed Apr 01, 2015 1:48 am

Oh bollocks, it's never the easy option. Sorry for getting your hopes up.

Could well be something shorted elsewhere... Have you checked the big electrolytics to make sure none are showing a dead short?

You can try a simple diode test of the bridge rectifier but I find they're usually pretty rugged. IIRC you disconnect the PSU from the rest of the synth via the molex connectors. Have you tried that and then checked the voltages?

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Re: JX-3P doesn't boot up / power supply issues?

Post by DesolationBlvd » Thu Apr 02, 2015 11:34 pm

Good news - 5V is now reading 5V again. It boots up and the front panel responds. Most likely, the front panel board is sound.

Horrifying news - I was greeted with a bloodcurdling descending sound. No response from the keys. 7V is now reading 10V! Turns out - I bought the wrong rectifier! 2W10 instead of W02...Quickly turned it off...

:oops:

Side note: I hate the mail-order monopoly even more than before, waiting for parts only to find I goofed up and ordered the wrong one. I now checked on a site and they say W02MG or NTE5304 are substitutes...Going with the first one.
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Re: JX-3P doesn't boot up / power supply issues?

Post by Dr. Phibes » Fri Apr 03, 2015 4:53 pm

From where I'm sitting the 2w10 is a superior replacement to the original! As long as the polarity is right it should be fine. Was the original bridge rectifier actually defective?

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Re: JX-3P doesn't boot up / power supply issues?

Post by DesolationBlvd » Fri Apr 03, 2015 5:32 pm

Dr. Phibes wrote:From where I'm sitting the 2w10 is a superior replacement to the original! As long as the polarity is right it should be fine. Was the original bridge rectifier actually defective?
That's what I thought too...I wonder if the different spec (the "2" before it meaning 2A instead of 1.5A) is causing the +7V line to now be around +10V?


The old W02 was possibly busted, there was blackening on its legs and replacing it caused the +5V line to go from +0.5V to the proper +5V.
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Re: JX-3P doesn't boot up / power supply issues?

Post by Dr. Phibes » Sat Apr 04, 2015 2:29 am

DesolationBlvd wrote:
Dr. Phibes wrote:From where I'm sitting the 2w10 is a superior replacement to the original! As long as the polarity is right it should be fine. Was the original bridge rectifier actually defective?
That's what I thought too...I wonder if the different spec (the "2" before it meaning 2A instead of 1.5A) is causing the +7V line to now be around +10V?
That's just the max amperage they're rated for so it should be ok. As far as I know the +7V is solely for the PG2000 programmer so as long as +5V rail checks out I'd put it to the back of your mind for now (I don't see much else you can do on that front other than increase the value of R1).

Working out why the keyboard is working or not is the trickier part. Why not try sending notes via MIDI to see if the the synth comes to life? If it does then the problem most likely lies with the key assigning circuit.

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Re: JX-3P doesn't boot up / +7V line issues

Post by DesolationBlvd » Sat Apr 04, 2015 4:35 am

Funny thing happened on the way to pick up my Moog MG-1 - there was a Radio Shack. I picked up a W04G, installed it, and still got +10V on the +7V rail.

After the BEEEEEEooooooowwwwww, the faint drone responds to patch changes and keys on the keyboard and over MIDI.

Hmm...I remember experiencing this back when my OB-Xa was dead. I think that problem was beyond my skill level...Or, is it oscilloscope time again?

Side note: As for the MG-1, it was pretty cheap but had the usual foam meltdown, and after further diagnosis, I identified MM5823N failures. I ordered the MM5823N clones from flatkeys.co.uk (thanks to the dollar being strong against the pound), and should be on my way...
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