Running OctoPrint on a Raspberry Pi3b+. Had an 8Gb Sandisk U10 (highspeed) SD card onboard. Cabled via shielded USB cable to an ANet A8, running a stock motherboard, but with the firmware upgraded to Marlin.
This setup has been running well for several months. Suddenly, out of the blue it wouldn't connect via serial. Thinking it was a glitch in the Matrix, I just rebooted the Pi (physically pulled the power, and restarted from scratch). I also cycled power on the printer. Also tried swapping USB cables. No matter what I did, I couldn't get OctoPrint to talk to the printer.
My thought was that either the serial port on the Pi or the port on the printer's board had died. I had a brand new, never-out-of-the-box Pi on hand, so I cabled it to the printer, moved the SD card to the new Pi, and plugged it in. THERE WAS ACTUAL SMOKE! I quickly pulled the power, and traced the smoke to the SD card, which was too hot to touch. I let it cool, then put it in a USB adapter and plugged it into a laptop, and sure enough -- nothing.
So, at this point, I have no idea what piece of hardware is actually bad, and I don't quite know how to proceed with the diagnostics. I had thought about cabling the printer directly to a laptop to see if they could talk, but I don't want to fry the laptop if there is something majorly wrong in the printer's USB port. I can gen up another SD card with an Octoprint load, but I don't particularly want to just plug it in to one of these PIs without knowing what caused the previous one to burn. I really don't want to burn up any more SD cards, and I sure don't want to burn anything on my printer.
Has anyone ever heard of anything like this? Got any suggestions on non-destructive methods to proceed?