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JX-3P lights up like a Christmas tree
MUFF WIGGLER Forum Index -> General Gear  
Author JX-3P lights up like a Christmas tree
wahee
hi all

Got an eBay special on a rather knackered JX-3P synth. No sound and all the LED's lit on power up.

So opened it up and did the usual.
Checked power supply rails -15, 15 and 5v all in spec.
Reseated all molex board connectors
Checked battery voltage - stable.
Noticed the volume control was wobbly and had several dry joints. Fixed that and I get a 2 second drone when the synth is switched on now.
Progress w00t

I have another working 3p so I decided to try and eliminate at least the control panel board.

Swapped the panel boards with a known good one. The panel turned out to be ok.
So the issue seems to be in the main board

I noticed there was no alternating signal coming-out of the DAC test point
On my working 3p, I got hi/low on the logic probe but on the faulty 3p - nothing. The DAC on these seems to comprise of a long single inline TL082D. So this may be a problem.

So trying to trace back from here with the service manual.
Will check CPU output etc later.

So was wondering if there are any classic issues with these synths or anything I should be checking.

I have swapped out some of the 4051's as these seem not be the most reliable IC's ever. Although they appear to be more involved in the audio section of the synth.
Just me
Sounds like a stuck pushbutton. Make sure they are all free. I was able to light mine like a dead evergreen powering it up with some books on top of it holding down some of the buttons.
wahee
thanks for the reply. I think it's more serious than that though. Port 1 on the CPU is putting out nothing. The crystal is working ok, but DAC is not pulsing. Checked the majority of the 74 loic and they are ok. Starting to think the CPU is bad.

Perhaps RAM
sutekina bipu-on
All the most mysterious synth problems I nearly gave up on were traced down to the keybed or button input board, so I think Just me is on the right track. I have seen a fair amount of threads about synth repair where people suspected bad cpu, bad ram, bad dac, etc etc etc, swapped them all and nothing changed, usually ended up being something else.

I don't think these machines are old enough we have to worry too much about dead cpu, dac, etc yet although old RAM is liable to start getting finicky.
wahee
hi
thanks for the ram tip! you were right.

just an update

Main no boot problems turned out to b the RAM chip. There was also a dead 4011 logic IC on voice 5 and a bad BA662. So all is now well with the 3P
BLX
Hi Wahee, I have the exact same problem on mine but I'm not technical. Is it possible to explain how simple it is to swap the ram over and where I might find this. Will try the button thing as well as B4 was always sticky.

Would be great to rescue this if possible.

Tks
wahee
Hi the ram chip is a TC5517APL
Easy enough to get hold of. I got mine on ebay for about five British pounds.
Desoldering the old one is tricky as the traces on the jx board are very easy to lift.

I did a YouTube video on the repair. It's not a professional video, but should show you where the chip is etc on the board

http://www.mindburner.co.uk/synth/JX_3P.html
BLX
Thanks Wahee, just ordered a replacement chip. Will check the video out as well but the whole page below is really useful

tks
wahee
no probs, if you need any more help just holler
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