TR 99 rock trap was pretty reliable if the rock trap pre load was set up correctly and the front drum micro phone was working. Lots of information in the Service manual about setting it up with the correct pre load and testing the microphone. If i remember correctly there is an ejection stone roller above stone trap which should be lowered in rocky fields to the point where it starts to limit capacity. In crops with little rock risk you can raise the stone roller up out of the way. example streight cutting peas at ground level set stone roller low. streight cutting tall wheat leaving lots of stubble safe to bring roller up. I had a 1999 model good combine except way over powered. Upper rotor drive shieve (torque sensing drive) can expand too much from a breaking snap ring.
If the door isn't set high enough the grain hits the lip and rolls in a ball creating pressure on the door to open it. The solenoid triggers it from the sound board so disconnecting it does not change anything. The feeder chain has to be tight enoung so it doesn't hit the door'. The manual is pretty good as to setting up