The symptoms of the problem is an I2C write error when running IMU.py sample program. But works with magnetometer code commented out.

 

This is a problem I have seen in a few locations with no answer and experienced myself. I have found a fix that is hopefully helpful to some people

 

The magnetometer has its own 1.8V power supply on the accelerometer chip.  The enable for the 1.8V Power supply (IC8) is controlled by the Overo module so does not switch on the power supply when not plugged in, and hence the magnetometer doesn't work or communicate.

 

To use the robovero without overo I put a 150k resistor pull up to 3.3V.

 

I'm hoping this will be weak enough that when I plug the overo in it will be able to control the line. If anyone knows more about the purpose of SYS_EN being controlled by the Overo it would be good?

 

Maybe this could be fixed in a hardware rev