OldSynths

Hello all, I'm trying to tune a voice on my OB-XA, and I would 
apreciate much your help. The problem is that the voice stays in tune 
in low frequencies but 2 octaves up the voice is out of tune, 
adjusting the VCO tunning pots of the voice card individually can get 
them in tune on high frequencies but then, when I play low notes these 
are out of tune. I don't know if my explanation is very good but the 
behaviour is like that voice doesn't remain in tune along several 
octaves. When playing this voice with two oscillators on high notes 
they also are out of tune between them, like a 2nd minor.
Any idea? Thanks a lot in advance.
Kind regards.
Miguel Mendoza.