Strange Thermal Runaway Error Behaviour
got my MK3S Kit a week ago, built it and started printing. It printed the first models well and without problems.
On longer prints i get strange "thermal runaway" errors.
Today i investigated this:
During an print i got the error again. All the red lights on the board simply went off and the temperature started to fall. Somewhere after a minute the "thermal runaway" error kicked in.
After such error the printer refuses to heatup again even if i turn the printer off and on again. The printer works again after 1 or 2 hours again (until the next thermal runaway)
The interesting part is: today i decided to upgrade the firmware (from 3.7.0 to 3.7.1-2266) during such a "refuse to heatup" phase.
Guess what after the upgrade the printer still refused to heatup and i still had to wait 1 hour to print and to get a thermal runaway again.
So after the last error i tried to preheat every 5 minutes wich resulted in preheat errors.
Then next strange behavior occurred: the printer heated the bed just fine but not the nozzle. this resulted in a preheat error.
The PSU had 23.9V on both rails all the time. I think it has to be like that.
I also tested the temp sensors: they work and the display shows the temperature change.
Where to look next?
I contacted the support. As suggested by them i printed with lower fan speeds.
max 60% and max 80% for the bridges.
It didn't help. The print failed after 75 minutes. But this time i witnessed the failure:
The temps were 216/215 and 60/60.
Suddenly the printer beeped and the temps went to 134/0 and 60/0.
The strange thing is that the temperature dropped during this short beep so fast without showing any values in between.
Again i had to wait somewhere of 1 hour to be able to print again.
My gut feeling tells me there is a cold solder joint on the board.
Looking at my failed prints i can tell the room temperature the printer printed in.
The warmer the temperature in the room, the faster the failure 🙁