ground loops

Hello Forum,
Thanks for the help so far.
I have an additiional problem with the ground of my development board. The RCM6700 development board has a 3.3V rail which I do not find very useful since most components (logic gates, amplifiers etc) operate on 5V. I therefore have separate 5V supply (from a battery) to power the components of my circuit, however I have placed connected the ground of the power supply and that of all components to the same ground of the board.
When the board is powered off, the correct voltages appear across all the components. However, when the board is on it is as if the ground is floating above 0V and I no longer have 5V from my battery power supply. Furthermore, if I turn off the the board, I notice that an LED stays weakly lit as if the RCM6700 chip is draining power from the 5V battery supply.
Does anyone have any idea what is going on and how it can be fixed?


I suggest you follow the schematics for the RCM67xx proto board