Casio MT-46/45 repair (melody keyboard)

[wax+wire]

Hi guys

just found a casio MT-46 (45s are the same basically) in a cupboard.  The 'accompaniment' works perfectly, but the 'right' or 'melody' part of the keyboard makes no sound what soever.

I openned the keyboard and all the wires looked fine (thought it might be a broken ribbon cable) and the PCBs all look good.  anythought on what might be wrong?  any leads on a service manual?

found a user manual on the net, just not the service one.  with a circuit diagram i might be able to follow the signal to where it should come from.

Thanks in advance