I feel with you.
Ofcourse it will boot fine when you bring it for service and then when you get home it won't...
It looks like some of the parts is at the end of it's worjing days, so somewhere in the future it won't boot at all..
I think the best place to get some info on it for simular behaviour, is the Solton club.
I placed the link below, just in case you don't have it.
There are a lot of very helpfull people on this list, so probably they have an answer.
http://www.angelfire.com/ms/synthmuzic/ good luck,
Fred
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76