I also had an old radio that physically, when trying to arm, the stick bumps the bottom right corner of the gimbal housing. This would prevent the yaw value from going above the maxcheck value until I pushed the stick up a bit. If that's the case on yours ... Then we will go to the client and lower the value of maxcheck to something that is below a yaw value that you comfortably reach with the throttle all the way down. Again if I were a betting man, I'd put my money on your stick hitting the housing of your radio.
In cli (you know the procedure by now)
set max_check = 1950