Vintage Synth Repair

I just took my Matrix 1000 out of long term storage (that means my 
closet). Works fine when first turned on but after a few seconds when 
playing a single note line (such as a bass line) I get notes that are 
softer than others (which doesn't happen until after being on a minute 
or so). I didn't get an owner's manual with it and would like to get 
that and a service manual if anyone has them. I'm figuring that the one 
or two of the voices are causing the problem so I plan to start 
troubleshooting there. If any of you have seen this problem please let 
me know. (Is there a way to get this thing into mono mode? I'm using the 
module for bass lines so I don't need polyphony at the moment.)

-- 

Steve Mays KS4KJ
5+6 String Basses
Fretted and Fretless
http://www.myspace.com/stevemays
http://www.facebook.com/SteveMaysBass
http://atlantapromusicians.ning.com/profile/SteveMays