So here’s a funny one I have an Odessey that only plays low C note when you press any key on the keyboard. If I press one key then press a second, the correct note plays spaced from low C. I have cleaned and polished the gold CV and gate rods and also cleaned the cat whiskers. Also checked all the 100 ohm resistors and connections. I measure 15V on the CV buss rod then press any key and it drops to 10.35V I press any single key and you get the same voltage 10.35V. If I press two keys then I get lower voltages that are roughly proportional.
I am about to go through the calibration procedure but thought I would ask in anyone has seen this.
Check out the schematic for board A-II in the service manual. It sounds like the keybed itself might be functioning properly and the problem could be in the “Keyboard Control Voltage Memory” circuit or perhaps the “Summing Circuit” (all on board A-II).
Does the pitch bend work? If it does then the Summing Circuit is probably fine and the issue most likely is in the Keyboard CV Memory circuit. You can check that the keyboard CV is entering the circuit at J2-2. Then check if you’re getting the sampled keyboard CV at the output of Z4 pin 8. If you’re not seeing the keyboard CV there then a component has failed somewhere in that circuit. Z4 is an LM1458 and it’s pretty common for those to fail in vintage Arps.
Also remove any tantalum capacitors that are between power rails if you haven’t yet, they can fail disastrously as the synth ages.
Thank you very much for the fast reply. Yes the pitch bend control functions correctly.
The thing that is different for me as I have repaired several Odessey’s the CV change when any key is pressed is the same. I expect the voltage to be different depending on the key pressed.