Vintage Synth Repair

Bo, Dennis, Grant.

to spot the source of the problem, you can try this first, disconnect the the keyboard connector on mainboard CN8 and CN9 (from main board to keyboard unit).
turn it on and tell me the result.

Please be aware of electric shock around the Power supply unit.

BR
Ichdar

Suzy,

i'm sorry for the late response, and i thought it was a keyboard engaged instead of panel switch engaged. The CN8 & CN9 connector disconnection is only to isolate if the problem coming from the keyboard (short circuit or ohters)

now, we need the detail symptom, all panel switch no response? all LED/lamp stay ON? any sound from the keyboard (notes) or any infos that lead us to the rigth diagnosis step.

Do you have any knowledge in electrical/electronic ? it's my pleasure to guide you, but the next step will require the medium electronic knowledge, testing with voltmeter, or even an oscilloscope to verify the test point signal.

I will be more easy if you have that knowledge since the tools is not a big constraints nowaday (there are so many DIY tools in web)

BR
ichdar

First article on top. Is the group moderator active? I posted a week ago and I still don't see anything.

Anyway JX-3P is a pretty straightforward synth usually.. If all the lights are on with anything I always start by checking POWER SUPPLY VOLTAGES. There should probably be a ground reference point ...perhaps the case on some units. Check for impedance (ie. with ohmmeter) to the case from the lower left pin (looking with the chip's pin 1 indicator UP and looking down on it from the top) of any 7400 series chip pretty much or 4000 series chip. I'm sure the JX series all had some :-)

If you get near zero ohms then the case is probably a good ground reference. Power the unit up and check all pins coming off the power supply board. (ie the one the transformer wires go to except don't bother with those probably as they are AC and you want to set the meter for DC first and see what's coming out of the DC supply lines. )

If you don't find plus 5V within a fairly tight precision, and plus and minus 12 or 15V then probably something is wrong there. Sometimes filtering /regulation fail and lines will have AC on them to the point where you can't get an accurate meter reading and you'll have to use a scope to see what's really going on there.

PS I try to accumulate all repair tips specific to a unit on the SD Synth Information Resource

pages. Click 'production synths' and manufacturer and so on.