I've a problem with my BQ i3 Hephestos.
I've noticed that in the last few prints that I've experienced some temperature drops every now and then. Yesterday, after 3 of a 4 hours long print, the hotend completely cooled down (I have Octoprint and from the temperature graph it was visible the exponential decrease to 25 °C). Apart from realizing that, evidently, I have not any cold extrusion prevention set up on my Marlin firmware (I'll surely fix that asap), yesterday I've shut everything down with the idea to try again today. This morning, though, I could not start my print because the heater didn't even warm up.
After disassembling the hotend I've tried the following things:
- I've tested the thermocouple putting it near the heated bed and it measures the correct value
- with a tester I've measured the voltage that goes into the resistance ($\approx 12\ V$)
- I've measured the resistance with the tester ($\approx 3\ \Omega$)
I've also noticed that while $12\ V$ is the voltage that the printer sends to the resistance, measured when the resistance is not attached to it, if I repeat the measurement with the resistance attached to the printer I get a few $mV$. I really don't know whether it is the expected behavior or not.
Trying to inspect the cables better I've noticed a black spot on the connector of my Ramps 1.4 board (as you can see in the attached image).
At this point I think I may have damaged something with too much current/too much heat. Too much current it seems strange to me because I have never changed anything in that sense, It is exactly the same as when I have bought the printer. It may be something related to the heat as the problem firstly occurred only on long prints (some hours).
I don't know if this clarify something to you, but to me it says almost nothing...
I've tried to attach the heater again to its original place and now it seems to work (in the sense that it gets hot). I've initially set the temperature to 60 °C, and it had no problem reaching and keeping it. Then I've tried to raise it to 180 °C but I had to shut down the heater after a few seconds because the cables became very hot and tender and it smelled of burnt