I purchased a Roland JX-3P with a PG-200 programmer from eBay in 2016.
It was advertised as working but once I got it I realised that it had a few faults.
The LFO trig button didn't light up and had no effect. I opened up the JX and upon further inspection,
found a bad dry joint probably from over enthusiastic pressure, on the little LFO switch board.
The PG-200 also had some issues. Several of the control knobs were faulty. Noticeably the filter, ADSR and volume pots.
The switches seemed to be ok though. I first of all checked to ensure the voltage lines -15/+15 were ok. After a bit of troubleshooting and research on the net, the culprit seemed to be a LM311 comparator chip above the write button. Another culprit can be a failed 100uf capacitor. This can manifest as a short on the +,- 15v rail. If the switches work ok but the pots are dead, then suspect the 311. Groups of pots not working can suggest a faulty 4051 IC.
Apparently this is a common fault with the PG-200 and may be caused by using an incorrect lead to attach to the 3P.
I decided to de-solder all the other IC's while I was there and fit gold turned IC sockets. I also replaced a few of the electrolytic capacitors as they had blown up a bit, and were perhaps leaking.
At the risk of stating the bleeding obvious here, If opening this synth, be very mindful of the exposed mains wiring and fuses.
It's all too easy to brush a hand past it and get a shock.
One of the keys started to not sound properly. I opened up the synth, and removed the keys surrounding the dodgy one. The springs holding the black keys are different than those of the white so keep separate.
This synth uses carbon contacts with rubber tops and a quick clean with some switch cleaner and all was good.
more about JX-3P's
.Here is a video on fixing one
The different sample and hold areas of the two main board versionsf the JX-3P board.
In 2017, I also installed the Organix midi kit, from River technologies. It's fantastic. I can now use both the PG-200 and MIDI. I can also permanently set the MIDI channel to 3. Responds to CC commands. Well worth getting and easy to install