Please see tracker issue 157 for the beggining of the story.
I think that there is definitely a PPM encoder problem.
I thought at first that my APM board was faultly. Chris kindly sent me a replacement board, a 1280 board instead of the original 2560. After connecting it, loading the latest firmware, radio setup and so on, i did again some tests.
After playing with the throttle stick, all was ok. suddenly after a couple minutes, i loose CH3 input again.
I lost it when i was pushing the transmitter stick quite fast to the max. Motors outputs stayed at a quite low RPM and no more possibility to change it.
After checking, my receiver output 3 was perfectly normal. Going to CLI radio test, i had no more Ch3 input.
Scope analysis have shown that when the problem exhibit :
1) the receiver CH3 output is always ok
2) the ppm encoder output is missing output CH3.
After resetting only the PPM encoder AVR chip, i get back CH3 input.
I think that there is definitely a problem with the PPM encoder. Certainly a software problem.
For those tests, i've used an USB isolator to be sure that there was no ground loop between the computer and the board.
The board was powered by a Castle creation BEC, at 5.1 V.
The reason of this malfunction is quite obscur, perhaps a variable overrun in the ppm encoder ?
If this occur during fly, this is assured crash.