Out of tune or out of scale?

Obviously the latter.
Playing unisono all voices are in the same tune. When playing a chord it sounds always detuned in the same way, no matter in which order the notes are played. So the voices are in tune to each other. It is just that the overall scale is wrong. This should be easily corrected by trimming the antilog function block. The service manual does not say that much about it, though.:

PS-006TN