Hello again Kai,

Yes, the switches are connected directly to the inputs of the 74HCT540.
Would it make much of a difference to have the switches pulled to ground while in the off state, then driven high when the button is pressed?
The reason I ask is that it is much easier to just solder in a 10k resistor network than swap the gnd/vcc lines on my button pcb.

The other thing is, I'm having a hard time understanding why not having the inputs pulled low in the off-state would cause the problems I'm having. Even when the buttons are pressed (driving the 74HCT540 inputs to 5v), the output (Bus) side isn't being driven low by the buffer.
Do all the inputs need to be pulled high or low for the 74HCT540 to function properly? I'm having a hard time believing the buffer is that sensitive, but perhaps I'm wrong.

I'll solder in a 10k resistor network to pull the buttons low in the off state tomorrow - see if it makes any difference.

Thanks alot for your time - it's much appreciated,

George Ricketts