Roland JX-8P Repair

[garytoosweet]

Hey,

I picked up a Roland JX-8P that wouldn't power on. Problem was a faulty IC on the power supply. Power supply rebuilt and stable.

I now have power but the synth is making random sounds that aren't totally correlated to which patch/preset has been selected.

Here's a video of the issue: https://imgur.com/a/lJMTwdz

The problem seems to be partially intermittent as I have had the correct sounds/notes coming out of it briefly.

First synth repair here so struggling with where to start.

There is also no Aftertouch, but I can address that issue after I figure this one out.

Service manual here: https://www.kiwitechnics.com/index_h...e%20Manual.pdf

Thank you in advance for any help.

[xtian]

Basic stuff: Did you measure the DC voltage output of the power supply, is it within spec and stable?

Try cleaning and reseating any jumper cables that can be unplugged, press any socketed ICs to reseat them, etc.

[The Dude]

I'm hearing a pitch bend and you also say you have no after touch. I'd be looking at connections to and checking power to the volume board since both of those functions are controlled there.

[Enzo]

I haven't seen one in a while, but when I see a synth making funny noises and features not working, the first thing I do is reinitialize it. Aftertouch not working? MAybe so, or maybe it is working, but the timing parameter or the depth parameter or the delay parameter has a corrupted number in memory that the effect isn't heard (depth) or takes ten minutes before coming up (delay). I recall Ensoniq ESQ1 when it was a hot item, and it would lose its mind and the envelope parameters got skewed, so you press a key and nothing. But if you held the key, over the next several minutes, the sound would slowly build in, because the ATTACK parameter was scrambled.

Still got at least 2.5v in the battery when power is off?

[The Dude]

I would not factory reset this keyboard unless you have a system disc with factory patches available. If memory serves, you'll have to reload all of the patches. I don't believe they are stored in memory after a reset. You'll have to find a disc with the factory patches and reload them.

[garytoosweet]

Power supply voltage is exact and very stable.

Volume board power is good and connectors seem tight, however after pulling the volume board and playing with it hanging out the issue seemed to stop. I've reinstalled the board and the keyboard is playing well for now. Possible could be one of the wires not connecting in the molex connectors.

I'm going to disassemble the keybed and clean switches and work on the after touch. Once that's done I will inspect the molex on the volume board and do a final testing.

This synth sounds really really nice.

[The Dude]

The connectors could just be corroded/dirty/not making good contact. When you unplugged them and plugged them back in, you may have inadvertently fixed the problem. Sometimes that's all it takes. However, you may want to give all the connector contacts a good cleaning.

[NateS]

JX8 aftertouch was really really weak from the factory. It might not actually be "broken". Could probably stand some tweaking.
And be super super careful putting that sucker back together. The plastic is brittle - I broke a number of the recessed screw wells - and that was probably when it was only 10 or 15 years old.

[garytoosweet]

Wanted to put closure on this thread.

The issue from the video in first post came back very briefly and I cleaned all contacts to the volume board as well as recapped it since it was out, and it's been permanently fixed.

Aftertouch circuit was able to be modified, increasing gain by swapping 3 resistors on the volume board and it is now working and responsive.

All the heat that causes issues in these units comes from the power supply. Seems like it would be a simple fix to change the +/-15V and 5V rails to use DC/DC converters. Just getting rid of the LM7805 would help immensely as it seems to be the biggest heat generator. Next time I will try it.

Thanks for the help. Great sounding synth.