The Yamaha YPG-225 has 4 ribbon cables attached to the keyboard. The keyboard is in two separate sections: The lower 33 keys (E to C) with a 6-wire ribbon cable going to the main board, and the upper 43 keys (C# to D) with an 8-wire ribbon cable going to the main board. These two ribbon cables carry octave sensing for groups of 6 keys, at most, across the keyboard. So if a group of 6 contiguous keys are not working, it will mostly likely be a problem with one of the wires in these ribbon connectors not making the connection to the main board. There are also two ribbon connectors with 12 wires. There is one short jumper ribbon connector between the two keyboard sections and one long one to the main board. These ribbon connectors carry key note information, all the keyboard "C" keys on one wire, all the C# keys on another wire, etc. So, if all the "C" keys are not sounding, it is probably a broken connection in one of the wires in the two 12-wire ribbon connectors. I was able to fix a problem on the upper...