I'm using this servo SM-S4303R. There is a link to the datasheet included. They're plugged into the board below which connects to arduino.
Had all four servos working, unplugged them, mounted them and tested and one was not working, due to being plugged in incorrectly. So, to see if this was the case, I plugged second one in same way to see what would happpen... Both don't work now.. I'm fairly certain I had Signal --> 6V and +Ve --> V- . Would 6v up the signal line cause this?
I've inlcluded some pics so you can see what I'm on about!
I would have thought this too although it seems likely I have somehow blown the servos.
Servo datasheet... http://www.oomlout.com/DATASHEETS/SERV-03.pdf