Patches and discussion for Ensoniq VFX family

I have an Ensoniq VFX-SD that belonged to my son who performed in a 
rock group and stopped using it when it would freeze up during 
concerts.  Now, I just love the sound of this thing, but had the same 
problem with it.  It would either tell me 'calibration error' or 
every note on the keyboard would start up with continuous noise.
So, about 4 years ago I took it to a repair shop, who charged me 
60.00 but said there was nothing wrong with it----he just didn't play 
it long enough to find out!  So---now I have moved away from there 
and it is much later---only played it a couple of times since, and it 
would do the same thing.  So I was looking on Ebay for another brand, 
but hating the idea of buying another and giving up on the one I like 
so much.  I don't know a thing about all that it does, I simply play 
it.   But, it's insides are a computer and I don't want to be erasing 
memory or whatever---but, I was reading online about people in the 
same boat who repaired their own----bad solder joints, etc.  Well, I 
just plugged it in, and now it is saying 'low battery'.  Well, the 
manual says to take it to an 'authorized dealer'.  What dealer?
I am needing to know how to take it apart without damaging any of the 
comuter works inside. On the back side, where all the jacks are, is a 
row of rivets, what looks like a continuous hinge---maybe the back 
drops down?---and black screws that hold it closed.  If I undo that, 
will it give me access to the batteries and the bad solder joints?  
Probably not---so, do I then turn the thing upside down and remove 
all the screws from the bottom and lift the bottom off?  And---I just 
noticed the new posting today that mentions a fan system that will 
keep the machine cool---would that be a thing to buy?  I really, 
really love the beautiful sound of this thing, don't want to give up 
on it and then buy a pig in a poke, so to speak.  Thanks for 
listening and I hope you can help------Dorothy