All about the Roland Jupiter-series

I need some help. For a while now my jp6 has had an intermittant 
problem where in poly or unison mode every 6th voice would crackle and 
change volume at random. After about 20 minutes it would usually fix 
itself and be perfectly alright.

Well today I turned it on for the first time in 2 weeks and almost the 
entire thing is frozen with no sound. The Bender board seems to be 
fine with the rate light changing appropriately, and same with the arp 
rate light, but everything else is locked solid. No buttons work, 
there's no sound, the main LFO rate light is on but not blinking and 
not changing speed like the others, and it just seems as if the entire  
thing is frozen. I turned it on again a little while ago and it was 
back to normal and working fine, although the main LFO was lit 
constantly, so I turned it off and then it froze again.

Does anyone have any ideas, or can anyone with the service manual tell 
me if there's a procedure to get it into some kind of test mode?

Thanks in advance.