JX3p-No sound-No front panel functions=could use some help p

[valvusmusicus]

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

[Uncle Krunkus]

I can tell you from working on my MKS-30 (JX3P in a box) that the "7V" line from the PSU is simply the input to the 5V regulator, and could be as high as 11V (in my case), and still be fine. When you trace it you'll find it only goes to the cartridge socket. I think it's used to "flash" the memory on those old cartridges. (EEPROMs) For the time, they were the most reliable way of storing and transferring data.

BTW If I were you, I would start by very carefully scrubbing the whole thing, to within an inch of it's life, with a hydrocarbon solvent, and a toothbrush.
Well, that's how I started mine, and it's a lot better than it was!
I've done a lot more than that though,.... it can get quite involved.

[valvusmusicus]

Thanks for that-I will give the boards a good scrub
I also notice that there ais a connection from PSU bd to main bd, thats not on the schematic, pcb overlay or anywhere in the service manual. its a wire coming from the output of the 5v reg on the psu bd and grnd to the main bd

On the PSU bd the connection is from accross D3 and c1. to the main bd accross c76-which I think is associated with the 74LS32 chip, which is IC53
Is this a mod? should I dis-connect it? Odd!!

Please see pics attached. The first one is the bottom RH corner of the main Bd and the second is the RH corner of the PSU board

many thanks

V

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[valvusmusicus]

Cleaned the main bd thoroughly, there was some crap on the bottom right corner of the bd-now all the preset lights are flashing randomly-but when you depress the switches-they do nt respond. none of the other switches/LEDs function
Guess itstime to clean the switching bd??

[valvusmusicus]

From info on another forum-seems there may be a fault around the DAC? will measure outputs/inputs/offsets, etc, tomorrow at work with scope
Will keep the post informed

[valvusmusicus]

DAC circuit is fine-seems to output data well, not latched up or dead with no waveforms-any thoughts please?