I don't know the unit, nor do we have a schematic. Must MANY keyboards or control panel switch circuits are matrixed, and to prevent false paths each switch has a series diode. Look at the keyboard circuit of any synth. And a matrix does not short a hot pin to ground, it has rows and columns that are shunted together by each switch. So without further information, any chance you put all your switches to a common while the unit circuit does not common them?