Diagnosed the problem by seeing the lower fan was not turning. Didn't have any squeaks or sounds as a warning sign... It just stopped working. Went to AppliancePartsPros.com typed in my make & model number (Samsung NE58F9710WS). The web site pulled up the parts schematic, I navigated to the part on the schematic (Assembly #8 - Assy Motor Convection-Re DG96-00110B / AP5580897) and ordered it "Express Shipping" because I need the oven for Thanksgiving. When the part arrived, it looked identical to the existing and I assumed it was the correct one. I installed it from the back, but when I went to attach the fan on the shaft from the front (inside) of the oven, the nut securing the fan would not thread onto the fan shaft. I had to remove the fan, and then I could see that the threads on the shaft of the motor were not the same as the previous part. I called AppliancePartsPros.com to ask if there was a problem. The person I spoke with put me on hold, checked, and when she came back on the phone, she said that I ordered the correct part from the Schematic, but the Schematic is incorrect. She said she could send me out the "Correct" fan motor (again "Express Shipping" hoping to get the oven fixed in time for Thanksgiving), but I would have to pay for the part in advance and I would be refunded for the first part when they received it back. So now I had to pay for two express shipping charges and a return shipping charge. When I received the 2nd fan motor, I immediately tested the existing fan nut (Left Hand Threads) and it worked! However, while replacing the fan, I noticed the tabs to receive the wiring harness were different, and the existing wiring harness would not work on the new fan motor. After "Splitting" the harness in two and adding some shrink tubing to keep things safe, the new part worked and I re-assembled the oven. Not the easiest repair ever, but I was able to finally get it to work in time for Thanksgiving!