I just had a similar problem with my C900. Basically the tray never lifted, and I was worried that the "tray lifting assembly" was faulty. But then I saw a fix for the Minolta MagiColor 2300 (basically the same machine?) which involved pushing down the tray to the bottom. This will supposedly trigger some reset of a solenoid connected to the paper lifting mechanism. I did this trick with my machine running - and it worked!
Now my C900 is picking up paper from the tray. I have seen similar solutions on the net, that you should fill the tray with as much paper you can, to get similar results. I think this (partly at least) is the same solution - filling the tray with paper will undoubtedly push the tray down. ;)
There is paper jam or there is the dust in some sensor
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