On my D180 auto pilot installation with two servos, the button which always would disengage and engage it (with a 3 second hold), will no longer engage the autopilot. The button has been replaced (thinking it is noisy). It will properly disengage the autopilot but it will not engage with a 3 second push. When one holds it for a long time, the AP text blinks on but will not stay on. There is no AP module, the servos are directly connected to the D180. Any suggestions?