My two year old upconverting Toshiba DVD/divx player from Woot.com wouldn’t eject my rented DVD (I am Legend). I would push eject and it would say “Open”, do nothing, and after a few seconds say “Loading” and play the DVD again. Once the harassing blockbuster calls started coming in I decided to try and fix it.
I found a great site called Fixya, which is similar to this site but focuses on hardware.
This page addressed a similar problem with the Toshiba SD-4990. That page linked to a service manual here (https://www.vancebaldwin.com/shop/research_new/TBA/SD4900.pdf ) which was similar enough to be extremely helpful.
Some suggested that it was a software issue and unplugging the machine for half an hour to let reset it self. However, after unplugging it all night the problem remained the next morning.
I took the machine apart (6 screws on the outside) and unmounted the drive (4 more screws), unplugging the three cables and remembering their orientation (blue wire faces the back). I unscrewed the top chasis (2 screws underneath soft rubber & glue) and got the DVD out. Then after some finagling I found the eject levers on the bottom (long slide switches) that opened up the DVD tray. I massaged the tray back and forth, and did the same with the laser mechanism on its track. The tray belt was in tact and there were no loose solder joints or wires. So I plugged the drive back in loosely (without reassembly) and plugged the power back in. Carefully, without touching any capacitors I hit the eject button and the drive tray started working again. It must have just been jammed. I unplugged the power, reassembled everything, turned it back on, and it’s back to normal!
This may not be the problem your SD-K850 or other DVD player was having, but perhaps these steps will help you solve your problem.