Never Seen this Before, Part Two.
Since I last checked in, new heater cartridge has been installed, Polyfuse has been swapped for real slow-blow 5A auto fuse, Marlin firmware has been re-downloaded, spare power supply has been swapped in.
And it’s still doing this. 
(Peak one was on old 350 watt power supply, next peak was from known good 480 watt power supply.)
Sure your max temp setting in Marlin isn’t too low?
It didn’t change over the last 6 months.
Looks like a board issue to me. If you’re using pronterface is it giving you an error at all?
Edit: just saw the octoprint logo haha. Still any error?
If Octoprint can show serial console raw text, then watch that and see what it says when it goes into shutoff.
There’s no message, but if I wait for temp to come up, then have the motors got to Max X max Y then back to zero, the temp drops while the carriage is moving…With the bigger, known-good power supply.
If I turn the part cooling fan on…it looses power while the carriage is moving…This is freekin’ wierd…and I’m not really in a mood to pull the Arduino/RAMPS out of the other printer, but it looks like that’s the next step.
wait … if you power the cooling fan on and lose power seems like there is a short in the cooling fan then. Try to disconnect the cooling fan and see what happens.
All the time your fuses are shutting power down for a reason, if it is not excess power in the heater of the hotend it has to be something else.
I get what you’re saying…but I don’t think it’s the fuses that are tripping. I’m leaning towards the controller dying because I’ve replaced damnear everything else…the last test was with a conventional fuse, and it didn’t blow.
I just wired in a RAMPS 1.4 controller and it had NO problem requesting 240C
Man did it again. Mark this down, I’ve replaced everything except the thermistor and the wiring loom from the top to the controller…I’m betting thermistor
What is significative is that both shutdowns happen at the same temperature. So I bet it is a thermal shutdown on your firmware. I cannot see the temperatures scale though (to see what temperature is causing this.
However, let’s assume that is the case. It may or may not a thermistor problem. If the termperature is too higher than you commanded, it may be the thermistor is ok but the mosfet switching the hotend resistor is dead in a shorted state (not uncommon) so your hotend starts to heat it up as soon as power is applied (this is easy to be ruled out though: apply power and see if temperature raises without you asking it so).
If you connect the USB to your computer and use pronterface you should see a MAXTERM error if it is a thermal shutdown.
But … don’t you have by mistake a too-low MAXTERM value on your Configuration.h,?
This is probably not a maxtemp issue because OctoPrint would actually disconnect in such a case (error from the firmware) instead of happily continuing to poll the temperature, and on the first attempt it also stayed at the critical temperature a short while before dropping off.
My money would be on a short or something like that. A look into the terminal tab to see if the firmware is reporting anything back or maybe even rebooting at the points in question might help to figure out the cause.
It stays at temp until the carriage moves…I disassembled the strain relief for the wiring going to the carriage to find that I still have a thing or two to learn about strain relief.
if it is triggered by carriage motion I would say you have a short in the wiring that only happens at certain locations. If there is a short, power will go down. If you Arduino is not powered from the 12V line it may continue working happily while you see temperature going down because you no longer have 12V (until the short is gone). If your Arduino is powered from 12V, it will be gone too, not responding to any message.
Decoupled all of the wires from each other, loosely held in two different places to avoid the print head and…printer prints. So yeah, there’s a short somewhere and I need to hunt it down. Any cool ideas on how to re-engineer the wiring from the top to the bottom of the printer?
