Message
Re: roland jx-3p huhhh?
2014-12-31 by sounddoctorin@...
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.