Maybe something here will help? http://sounddoctorin.com/synthtec/roland/juno60.htm

Have you confirmed that the headphones get a stereo signal? If nothing else, I would try doing a factory reset.

I've got a Roland XV-5080 with maxed RAM and great (apart from a couple of very small scratches to the top panel) - Looking for an even value trade, but would consider cash+trade. I'm primarily interested in trading for (analog and/or hybrid) synths, but let me know what you have!