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 Forum index » Instruments and Equipment » General Discussion
Roland JX-3P Panel Board Issue Could Use Some Help
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totalreality



Joined: Jul 02, 2012
Posts: 4
Location: brooklyn, ny

PostPosted: Mon Jul 02, 2012 2:15 pm    Post subject:  Roland JX-3P Panel Board Issue Could Use Some Help
Subject description: Panel Board is Malfunctioning Voltage Issue
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Hi

i am a skilled DIY synth Builder but am not a certified repairman and am having difficulty fixing this synth.

There are 3 voltage going to the panelboard, -15, +15, and +5, for some reason the +5 is reading -5. What could cause this? The panelboard is not powering on although the LFO trig on the far left lights up when pressed. Also The PSU Tranformer is humming loudly.

Any Suggestions Would be greatly appreciated

Thanks
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DES



Joined: Feb 28, 2003
Posts: 677
Location: Oxford, NJ
Audio files: 6

PostPosted: Tue Jul 03, 2012 9:47 am    Post subject: Reply with quote  Mark this post and the followings unread

First thing I would do is check the multimeter and make sure the settings and leads are correct Very Happy (this has happened to me before, lol).

Have you traced the 5v back to the power supply? Check it there and make sure the 5v (digital) ground is good from the p/s to the front panel. Some gear will use a seperate ground for audio and for digital voltages. Back in the day this was done to keep digital noise out of the audio.

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grantb3



Joined: Jul 31, 2009
Posts: 23
Location: USA

PostPosted: Tue Jul 03, 2012 4:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Almost every single JX3P panel repair I have done has been to fix cracks in the traces on the board. Inspect the board closely and jumper any cracked traces with wires.
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buildafriend



Joined: Jan 30, 2011
Posts: 46
Location: New Jersey, US

PostPosted: Thu Jul 05, 2012 2:18 pm    Post subject:   Reply with quote  Mark this post and the followings unread

Thanks very much, will do. (PS I am working with the original poster on this repair )

Cool

Last edited by buildafriend on Thu Jul 05, 2012 2:25 pm; edited 2 times in total
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buildafriend



Joined: Jan 30, 2011
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Location: New Jersey, US

PostPosted: Thu Jul 05, 2012 2:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I did measure from the PSU ground.. that could explain things.

the +5V rail for the control board was putting out something around 3.75V which i think should be sufficient..

I want to recap the whole thing but i don't know if its really worth it. I could probably find a junker and just steal the control board but my first priority is saving money.
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grantb3



Joined: Jul 31, 2009
Posts: 23
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PostPosted: Thu Jul 05, 2012 2:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Recapping is a total waste of time.

Measure the power supply voltage at the power supply. Unplug the circuit boards from the power if all the rails don't come up.

If the power supply is OK by itself:
Measure continuity from each supply voltage to the extremes of the panel board (with the AC unplugged). +3.75v is useless. It needs to be +5v +/-10%, maybe even 5%. Same with the +-15v or whatever it has. Download the schematic and PCB layout.
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DES



Joined: Feb 28, 2003
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PostPosted: Thu Jul 05, 2012 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Agreed. 3.75 for digital circuits is in the grey area of operation. i.e. it might be a "1" or it might be a "0" depending on the circuit using it. Best make sure the 5v is just that. It might be a bad 5v decoupling filter cap on one of the boards.
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buildafriend



Joined: Jan 30, 2011
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Location: New Jersey, US

PostPosted: Mon Jul 09, 2012 11:49 am    Post subject: Reply with quote  Mark this post and the followings unread

grantb3 wrote:
Recapping is a total waste of time.

Measure the power supply voltage at the power supply. Unplug the circuit boards from the power if all the rails don't come up.

If the power supply is OK by itself:
Measure continuity from each supply voltage to the extremes of the panel board (with the AC unplugged). +3.75v is useless. It needs to be +5v +/-10%, maybe even 5%. Same with the +-15v or whatever it has. Download the schematic and PCB layout.


Okay, so forget recapping.

I still dont know what voltages I am looking for at the PSU. I see that all 3 rails are coming in at the point but I don't have numbers..

I am getting like -2.75VDC now... and I have checked that I am measuring from the correct ground.

Last edited by buildafriend on Mon Jul 09, 2012 11:56 am; edited 1 time in total
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buildafriend



Joined: Jan 30, 2011
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PostPosted: Mon Jul 09, 2012 11:51 am    Post subject: Reply with quote  Mark this post and the followings unread

DES wrote:
Agreed. 3.75 for digital circuits is in the grey area of operation. i.e. it might be a "1" or it might be a "0" depending on the circuit using it. Best make sure the 5v is just that. It might be a bad 5v decoupling filter cap on one of the boards.


Digital logic is not my field of expertise..

If I post the schemo, could you point out the decoupling cap? I could easily replace it.

thanks in advance and regardless.
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DES



Joined: Feb 28, 2003
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Location: Oxford, NJ
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PostPosted: Mon Jul 09, 2012 6:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Post the schematic and we can take a look at it. You should be able to find the different voltages on the schematic...follow them to components you can find on the board and carefully do your measurement there. Decoupling caps are usually near the logic or digital chips that the 5v supply is feeding. Some circuits may also put filter caps near where the power hits the board.

Did you look for cold bad solder joints and traces yet?

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buildafriend



Joined: Jan 30, 2011
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Location: New Jersey, US

PostPosted: Mon Jul 16, 2012 7:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

You guys are the best!!

Okay so the 5V trace is feeding a logic chip. For my knowledge, the repair set aside, is that pretty standard?

So, we checked out the PSU, we found some funky stuff going on. I think it might be the regulator or the bridge rectifier. we wrote down the strange voltages here:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

We plan on replacing all of the parts that come from the power xfrmr that lead to the control board. Can you help us source parts? Smile Smile Smile

____________________________________________________________

Here is what we did:

we replaced c19 and c22 in the control board.

Here is what we almost did:

we almost replaced TR19, TR20, TR21, and TR22 in the LED matrix.

We were looking at replacing TR4.
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DES



Joined: Feb 28, 2003
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Location: Oxford, NJ
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PostPosted: Mon Jul 16, 2012 9:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

First have to ask - did you check fuse F1? Smile

Before you make any changes, pull leads for testing, etc., you need to be careful with working on the power supply. The AC mains coming into it can kill you. So, observe saftety precautions whenever working inside the synth. Always turn the JX off and unplug it from the wall whenever removing connectors or lifting leads. NOT doing this could injure or kill you or damge the synth more....

Carefully look at the power supply board for any components that look like they have been running very hot. Usually they will be discolored when compared to other similar components. This might help you to isolate where the problem is.


Ok, before replacing anything you want to definately isolate where the problem is at. BTW - did you also check the +/- 15vdc lines? Good to do so before undertaking anything further just to see where you stand.

Next I would do a quick check across the bridge rectifier (D4) AC inputs - should be 9vac or pretty close - might be a bit higher. If not, you might have a bad transformer or bridge. If you pull fuse F1 you should be able to isolate the transformer from the bridge - should see 9 vac or better where the transformer comes into the board. If so and after putting the fuse back in and voltage drops, it's probably a bridge rectifier issue. However, before assuming anything further, turn the power off and unplug the synth from the mains (AC) supply and disconnect the power supply from the rest of the synth that is connected to CN1, CN2, CN3 and CN4.

Plug the synth back into wall power and turn it on.
Now check the 5vdc and see what you have. If ok, then something that connected to one of the CN connectors is flakey. To isolate, turn power off, unplug from wall, plug CN4 back into power supply, turn the JX back on and test. If good repeat procedure and add the next CN plug. Eventually one of them will cause the 5 volts to drop...that board would be the next place to check.

What concerns me is the +7v on CN4 showing 2.9v...that comes directly from the bridge thru a 10 ohm, 3 watt resistor. If the voltage is consistantly low it points to something that could be affecting the 5v regulator and 5vdc as well.

If the 5vdc was still bad after removing all the CN connectors, check across the input to the 7805 regulator - should be ~9vac. If low - say 2 or 3 vac, you may have a bad capacitor C12 (normally if it shorted you would have 0 volts there...but strange things can happen) or the IC regulator, IC-2 could be bad. Or, the bridge could be bad. You can try doing a resistance check across the cap and see if there is a short or very low resistance (make sure power is off and JX is unplugged!!) If a low resistance shows up, try lifting one of the capacitors leads and see if the voltage comes back up when powered on. if so, bad cap. If there doesn't seem to be a short across the cap, lift the input lead to the 7805 or just pull the IC - whichever is easier. Plug the JX back in and power up - check the voltage across C12 (the input to the 7805). If it jumps up to 9vac or better, you have a bad 7805. If not, power down, unplug and reinstall the 7805. Check the bridge rectifier, D4.

If the bridge is out Very Happy look on the side of it for manufacturer part numbers. You can probably get a suitable replacement thru Digikey or Mouser or one of your favorite parts suppliers. If you can't source it, put the number up here and we can try and find it. The 7805 should be able to be found just about anywhere electronic parts are sold. Same with the capacitor C12.

Well, try this and see if it helps and keep us informed. Also ask any questions that you need to. Above all - STAY SAFE!

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DES



Joined: Feb 28, 2003
Posts: 677
Location: Oxford, NJ
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PostPosted: Thu Jul 19, 2012 4:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Any updates?
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buildafriend



Joined: Jan 30, 2011
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Location: New Jersey, US

PostPosted: Mon Jul 30, 2012 11:07 am    Post subject:   Reply with quote  Mark this post and the followings unread

we will probably get to sit back down on and work on it this week.
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valvusmusicus



Joined: Nov 06, 2009
Posts: 56
Location: Bournemouth. UK

PostPosted: Sat Dec 08, 2012 10:15 am    Post subject: JX3P fault Reply with quote  Mark this post and the followings unread

Hi All
I also have a fault on a JX3P
Hi all
Have a JX3P-all the power rails are correct-measured on the main PSU bd with the rest of the synth connected, and at each bd on the molex connectro-so power seems to be getting to the synth at the correct voltage.
The only problem is that the 7v rail sits at 9.4v, eith or without the synth power looms connected-could be relevant?? -but the switches dont do anything(accept memory switch 3 is permanantly illuminated) battery is a bit low-but this should not cause this problem,....should it??
The battery only backs up the memory-has no effect on the unit booting up..?does it?
Any thought


All the best
V
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