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?
In a case like this, I try to become someone like these guys. Think: "if I wanted to get smoke from a microSD card, what would it take?" Imagine that you want lots of hits on a popular youtube channel and smoke equals ratings. The first thing, then, that comes to mind is that I would plug the Raspberry Pi into a 24V power adapter CAR BATTERY. Imagine 12V @ 100A. Oh yeah, that would cause some sparks.
So now, back to reality. Power is voltage times current. It would take a fair amount of power to toast a microSD card. Concentrate on power delivery.
Using a multimeter, measure the A/C voltage at the wall socket. Yes, it could actually be the power in the wall. If you're in the states, the highest the voltage should be is about 118V AC but it will usually be a little on the low side of 115VAC.
If you have a UPS inline to your Raspberry Pi's adapter, check the output of the UPS.
Check the Raspberry Pi's power adapter. It should be very close to 5V DC.
Check the power adapter's cable where it's connected to the blocky part. There's should be no nicks anywhere in the cable and no damage at the part where the cable goes into the block. There should be no damage at the micro USB end either. This is the most likely area where something could have been damaged and caused the problems.
Be careful. Something within this system isn't working correctly from the standpoint of wiring. Imagine frying your laptop. I wouldn't keep troubleshooting this by merely plugging things here and there. Mark that new Raspberry Pi. It could be the single piece in all this that has a bad soldering joint or whatever.
Actually, I've had this exact problem once. It turned out that I had bent the SD card at some point while trying to plug it into that really inconveniently placed socket on the controller board
Pull the card out and give it a wriggle, I'll bet you that it'll twist in one direction or another
On mine, it didn't matter which Pi I plugged it into, it smoked
Mine was busted right in half, I just didn't notice til I started playing with it "Gee, I don't think that this card is supposed to bend like this"