I am having some strange problems with my Blade after replacing just about every part that can be. Started with tail motor going bad. After putting in new one, heli started surging up and/or down with no control input. I checked out all parts and only thing I could find that may have been an issue was one servo that seemed to be binding somehow. Other servos are very easy to move, but one will take what I consider an extreme amount of force to move a minor amount. I replaced that servo, but problem did not go away. Checked new servo and it seems it is now taking lots of force to move, but once it starts moving, it is fairly easy, same as the others. Find it strange that a brand new servo would act like that, but could that somehow be causing the up and down movement of heli?

Try this, Unplug the main and tail motors from the four in one unit. Power up the helicopter and throttle up. Watch that all three servos move together and the same amount. If they do, you may need to look at rotor head and or blade pitch.