I have a Johannus Opus 230 with a fault. A Makin engineer looked at it for £250 but said it would be too expensive for him to spend any more time on it. Here's the problem: On the Swell the whole octave below middle C not sounding on any stops. When stop 34 (Celeste), 41 (Tierce) or 42 (Sesquialter) is put on there is a cipher at the pitch of G# below middle C. The blank octave transfers to the great when Swell to Great stop is used. Above and below the blank ocatave the Swell works correctly, as does the whole of the Great and the Pedal.
Could I get a circuit diagram, or could someone identify where the fault may be?