HK 328p

[JT]

 I';ve built a tricopter frame for my mate and he has bought a HK 328p for it. We put it all together this morning but the servo wouldn';t move when it was powered by battery(through the ESCs ubec). With the usb plugged in the servo moves a treat. Does this mean the 328p needs an external power source other than through the ESCs to work the servo? Everything else is working as it should.

Anyway to help out I gave him the crius off my quad to get him going which works fine(I';ll just play with my tri while the quads out of actoin lol)

[JT]

 No one?

[Hands0n]

What arrangement and ports do you have the three ESCs and Servo plugged into?

They should be like so:

[attachimg=1]

[JT]

 Everything was put together correctly as per the diagram you linked. The motors spun up really well it was just that the servo wouldn';t move (it would try) when powered by battery only. It would work if the yaw stick was moved really slowly or the board was plugged into USB and it would work a tiny plastic geared servo we had.
  I also tried my identical servo with the same results.  It was as if the board couldn';t provide the required power despite the 3 ESCs each having a 3A rating for the UBEC. 
I have seen tricopters on youtube that say they have a 328p and have seen no mention of the need for an external power supply for the board??

[Hands0n]

Just a thought - have you tried the Servo in another port than Yaw? - perhaps try it in Pitch or Roll to see if the relevant stick will move it.   Basically trying to identify if it is a problem relating to the single port itself or perhaps more universal across the board.

Sounds like perhaps a board fault - likely in the power train fed by the ESC.  Could be as simple as a dry solder joint.