KK2 HC receiver test problem with TH9X

[1-2-3-calum]

I'm having problems with my Flysky TH9X and the KK2 HC board. When I look at the receiver test screen the values are none zero, they fluctuate, averaging around 40-30. Even with sub trim and trim on the transmitter I am unable to move them far enough towards zero. The transmitter worked fine on my fixed wing models. This is my first attempt at a multi-rotor. Is anyone able to understand this problem or suggest a solution? Thanks.