Occasionally, I have to clean and lubricate the graphics cards' fans on my mining rig. As it is an open case, dust can easily get into the parts, and I have to go in there with some keyboard cleaner and oil. The reason for the open case is because it is a lot easier to make changes to the rig when upgrading or when diagnosing problems. The other reason is that there is a lot of heat generated from multiple cards and it is harder to fit so many cards into a closed case (there exists GPU server chassis, however).
Recently, I found one of the cards had a stopped fan, and it was not responding in the mining software. I thought it just needed a little cleaning and lubrication to the fans, but this was not the case. It turned out the fan motors themselves had burned out. I found a replacement online, and installed it:
Here is the rig back in operation!