Last post a ended with the question "So what do you do when you are sitting there with a so-so working printer, lots of failed prints, intertwined with a bunch of really successful prints?"
Well you turn to hot-rodding your printer. Many 3D printer owners will print parts like support blocks, new feet, maybe even a part cooling duct. These are all good things to print, but don't change the printer much. You see, the non-structural parts are the items that need the most attention. Items like hot ends and nozzles, multi geared extruders, higher torque stepper motors, and a more powerful control boards.
Most the these things mentioned take you down the path of having to learn the firmware that runs the machine as you will need to update and change certain specs to make the machine work. Who wants a printer that is supposed to move 20mm, and it moves 25mm. That just won't work.
The control board has been the best upgrade I have made towards a more consistent better controlled machine. The control board is literally what makes the 3D printer work. It takes the instructions read from the source file, interprets the details, and tells the printer where to go, how fast to go there, and how much material needs to be pushed out.
While it is the best upgrade, it is also the most involved upgrade. If you want your 3D printer to unquestionably always work, you must invest in a high quality control board. The stock boards that come with most Chinese printers have 8 bit processors. The last time I heard about 8 bit processors was back in the 80s with Nintendo. So these boards are very under powered and unless you print at slow speeds. Printing at high speeds will result in the processor lagging behind the print timing, causing errors that will affect print quality.
Duet3D make some of the highest quality control boards for 3D printing. Pictured here is the $250 Duet 2 Wifi. This control board has A LOT more processing power. It's backbone is a 32 bit processor. This processor will complete all its calculations long before the print is close to catching up. So you can print faster, with more complicated settings.
To be able to set this control board up with your printer you will need to know how to wire it, set up its wifi control, and build its firmware from scratch. It can be tedious work, and likely require troubleshooting during the process.
But when completed successfully, you will have a machine that works so much better than the one you bought. It will run cooler, faster, and quieter. Your prints will come out with better surface quality, and more consistent finishes with less defects and failures.