Turning on my Prusa i3 mk3 hotend causes printer to restart
tl;dr I have a printer that keeps restarting everytime I turn the hotend on (thing that heats the material). After taking it apart, nothing looked wrong with any wires or connections. I'm suspecting the power supply to be failing, but I have yet to check it (how would I even do that?). I want to make sure I get everything right before I go and buy a new hotend or power supply.
Hey there! I have a Prusa i3 mk3 that I've been using for quite a while now- at least a couple of years. Iirc, it has about 50+ hours of print time. For context, I am pretty experienced with these 3d printers and have a couple of years of fixing things in general. I also have all of the basic tools any good repair person would need: a soldering iron, multimeter, plenty of screwdriver bits, pry tools, etc.
Just recently, I was running a calibration when the printer suddenly restarted itself. I went to check it, and physically, nothing looked wrong. So, I decided to run the calibration again, and the same thing happened. This time, I noticed that it only happened after the hotend (the thing that heats the filament) was turned on. After manually turning on the hotend, I confirmed that it was the problem.
I found a guide on how to replace the hotend and followed it so I could get the part out. Throughout the guide, I didn't find anything wrong. There were no blown parts on the Einsy board, the wires weren't cut or crimped, and they were plugged into the right ports.
After finally getting the hotend off, it didn't seem like anything was wrong. For reference, the only things that go to the hotend are the heating element wires and a thermosister to check the temperature. The metal block looked good, and the heat sync looked perfect. There was only 1 thing I noticed that could be weird. The heater wires at the hotend kind of looked like they were touching, which could have been shorting, but they were stuck in their place when built, so nothing could have moved to suddenly short the printer. I wish I knew exactly how it heated the block, but that seems like it probably isn't the problem.
I then unplugged the heating element and not the thermosister, set it to turn on, and it didn't immediately restart. This tells me it isn't a software issue with the thermosister saying that the printer is overheating (again, the printer would restart as soon as the temp was set, not after a few seconds of heating).
My main (and honestly only) suspect at this point is the power supply failing. Is there a way to check if a power supply is failing or not? Or is there something else I should check/do that I haven't done? I want to make sure I know what the problem is and if I can fix it before I go replace the hotend or power supply.
Sorry for the long read btw. I'm happy to give more details if needed. Any responses are helpful!
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Update: After opening the bottom part of the PSU, the part with all the screws holding the wires in place, I can confirm the the PSU is not the problem. When I turn the hotend on, the power LED does not turn off and then immediately turn back on, it stays on. This means that the PSU is not suddenly shutting down when under load and then causing the printer to restart. This is kind of annoying, because it means that the problem very well may be the hotend.
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