Vintage Synth Explorer Forums

hi!
I have a problem with the tone select buttons on my JX-3P.
Button 1-8 in the row don´t work, 9-16 are fine.
The problem is always the same when i select the different soundbanks
or the sound edit modes, the buttons 1-8 are dead.
I´ve already checked the switch matrix on the control-panel board.
I couldn´t find any damage there. All the switches are working,
when i test them with a meter they connect/disconnect as they should,
the LEDs on the switches are fine, too.
I believe that there is a problem with the ICs that are between the
synthesizer circuit and the switch matrix, but i don´t know how
i can track down the failure there, because i not a professional
technician. my kowledge about electronic is very basic.

Does anyone have experience with that problem and can tell me
on which specific IC the failure could be?


Thank you!

cheese nucleus

1. check the cable and plug(s) from the switch board to the main board. Called MAIN CN6 - has 9 pins

2. IC 34 is a 3-of-8 decoder to scan the switchs . It's an LS138 - should be easy to find a replacement. this IC is located on the main board.

do you have a scope? even a data probe?

you should see pulses on pin 15 of IC 34... the same pulses should appera on one side of each switch 1-8... if no pulses, suspect IC 34.

thank you very much for your advice, rhino!
now, i found the failure. fortunately it was just several tracks on the panel pcb that were broken.
i fixed it with some wire, no problem, the jx is like new, again! i´m glad that i didn´t have to change
a mainboard ic.

cheese nucleus