Esc not working.

I have an ESC driving a brushless motor.

The Nano or Rx is powered from the ESC via a BEC.

It works fine when connected using my spektrum Tx/Rx combination.

Using a nano it does not.
Scoping the signal shows no obvious timing problems.
I do not get the usual start up tune either.

Any ideas, ? I suspect it is power related but not sure.

The BEC gives 5.2 volts.