--- In
yamahacs80@yahoogroups.com, "mborish_2000" <mborish_2000@...> wrote:
>
> I think that I might have the same problem. My keybed acts funny from the top key down to the C#. It will trigger, somewhat strange noises, if I have another key pressed in a lower octave. Is this the same problem? How did you troubleshoot it and fix it?
>
Have you verified it is not a problem with a particular voice card? If the problem isn't in the voice card, take a look at the KAS schematic (either the separate one or the full sheet layout). You can see how the keyboard data is sent into the YM26600 and then to the 26700.
What I do is verify that known good data lines are working and see the values and then compare to the problem lines. Monitor a particular note (like C) and press each C key in the octaves and watch the voltage change. If there is a problem in the keyboard itself, you'll see bad data coming in for the top octave. Probably it will be good though.
Next take a look at the N and B lines and verify that the are carrying the correct encoding for each key press. Finally, take a look at the CH 1->8 outputs on the 26700 and verify each channel is putting out the expected voltages.
Take notes along the way and the voltages seen so you have a reference if you ever have to go back.
If the D/A is really bad, you'll see consistently bad data coming from the channel outputs. Sorry I can't be more specific, but that's kind of the nature of debugging - probe around, take measurements, make 1 change at a time, break the circuit down, and repeat until the problem is isolated.
Because the CS-80 often strings connections through multiple boards, sometimes a problem downstream manifests itself earlier in the chain and you only discover it when you unsolder the connection and isolate one board at a time.