Hi ,
the setup is the following,
3s LIPO battery into one of these :
http://www.ebay.co.uk/itm/Red-LM2596-DC-Buck-Step-Down-Voltage-Adjustable-Converter-Power-Module-Regulator-/291054073365?clk_rvr_id=630997706073
(not exactly that , but near as dammit)
I have that set to 5.5v and power goes directly from it to the Rc Rx, which has a 5V rail and a ground rail, these rails go directly to the servos power.
The onboard voltage regulator for the Rx measures 5.5v on the input (what i suppose is the input) and the output varies between them, the three modules with working regulators measure 4.5, 4.5, 3.5
(Curiously, the lights on the modules with 4.5v blink faster than the 3.5v module)
I have traced the output of the onboard regulator back to the chip on its input pin, and the voltage doesnt change, so all looks ok.
I guess something else on the board was damaged.