Vintage Synth Repair

I have 2 of the Roland AT10s,  one home and one in rest home where
I play lunch music. After about 18 months  they both developed a raspy
sound in the lower manual.
I paid  $ 70 for the local Roland tech to look,  he obviously didnt
know what to do said he would get back to me, after calling admitted
he didnt know what to do. I did find a Roland national Sales person
but she couldn't help eother. The orginal dealer  stopped carrying the
line. 

I've been playing them thru the headphone jack into a guitar amp
since.  I'm hoping someone else would have had same problem and found 
solution.   

Tom Thornton, North Jersey USA