For a time now the preset “5” button on my JX-3P has not been working. I’ve been laying off this repair as I’ve had other stuff to do, but today I decided to do something about the matter.
Initially before opening the unit, I thought the button itself had simply failed. I tried measuring whilst pushing the button, but to my surprise, the multimeter beeped when measuring between the two contact points on the switch.
Next thought was that the switch was not operating correctly due to corrosion. I gave it a quick spray of some generic electronics spray, measured the button again, and then put the synth back together. Sadly the button still did not work.
Next step I did was to measure the traces going to the button. Between the button and the key-matrix, there was a diode. Upon measuring the diode, I found it to be faulty. I found another spare in my junk box, soldered it in, and crossed my fingers. Luckily that did the trick, so I put the synth back together.
I had to put the new diode on the other side of the PCB as the legs were cut too short, but it fit no problem.
Just a quick tip for anyone who might stumble upon the same problem, as it is not necessarily the switch itself which is the culprit.