Combines 1688 helpIJ

I think the items you refer to with slots are the Slotted Grates. There are 3 of them and they are located under the rotor behind the 3 concaves. I'm not familiar with the solid grate you refer to, but I vaguely remember that it may be helpful in crops like sunflowers to help keep trash off the chaffer when you don't need much seperation area. However, your problem with chaff in the bin is primarily due to uneven air flow from the fan. Go to this link and it will explain the problem and how to fix it. An alternative that will likely also work is the Airjet chaffers in the left link bar. I feel the deflector sould be standard equipment on any Axial Flow in cereal grains, regardless of other equipment selections.

This sounds like an air blast problem to me too, provided your sieves are in proper shape. Check your fan speed, belt, and drive. You shouldn't have the solid grate in for these grains, but if anything it should contribute to rotor loss and less chaff on sieves.