I have had an Ender 3 Pro for over 3 years. A year and a half ago I replaced the main controller board with the v4.2.7 silent board. I was surprised how much that lowered the noise from the 3D printer. I have also added more parts like the auto leveling bed probe; doing this had me compiling my own firmware to make sure all the add-ons worked.
Everything was great until recently I smelled a bad smell from the printer. I have gotten an enclosure over the holidays and thought it may just be I wasn’t used to the smell so concentrated. After it went on a few more prints I started searching to see if anyone else had this happen. It was a much worse smell than the normal PLA smell. After searching the Ender 3 subreddits, I found posts talking about how the terminals can melt.
I opened up the controller compartment and was shocked to see how badly the terminals had been melting! Apparently, the wires are tinned and overtime with the movement of the printer and work their way out of the terminal. This leads to the power arcing and melting the plastic. The suggested fix is to replace the terminals (or the board), and then install “ferrules” on the ends of the cleaned cables.
I contacted Creality for support, which they redirected me to Amazon, and opened an email chain, which Amazon never responded to. The v4.2.7 board was $30, I bought a new one to not deal with all of that. When I installed the ferrules and the new board it came right back up. Then inserting my SD card, which still had the last firmware I made on it, brought the printer 100% back.