Temperature of the nozzle rising uncontrollably - BTT SKR 1.4

Hello, I have a serious issue with my printer, namely two days ago during printing I saw a flash of light and some smoke coming from the motherboard (btt skr 1.4). I immediately unplugged the cord and inspected the board, but couldn't see any obvious damage. It happened fast, but I am pretty sure that the problem (smoke, flash of light, spark) occured around the black coil with "150" written on it (I am actually really green in the topic of electronics so I can be mistaken what it actually is). Anyways I chose to inspect if the board is dead and found out that it still connects to the computer and that for example I can still control the movement of the nozzle. However, a moment later I spotted smoke again, which turned out to come out of the nozzle (I am guessing from decomposing PLA). When I looked at my PC the "nozzle temperature" read around 300 deg. C. I confirmed with a reset, that it was not a matter of wrong manual input in Pronterface, but rather spontaneous occurence. The problem persists: whenever I plug in the 12V power unit to the grid the nozzle immediately starts heating up. I realize, that there can probably be a dozen of possible reasons, but I am hoping that someone had a similar issue or just any idea what happened and how to fix the problem. Sadly my search for "spontaneous heating" was unsuccessful. Maybe at least someone can determine whether this heating issue is a direct outcome of the primary issue (I am guessing overcurrent) or maybe it was the source of the problem to begin with and it just damaged board once the current got too high as a result of trying to further increase the temperature.

One thing I should mention. I have been printing for quite some time without issues, but I recently added an inductive probe (6-36V), that needed to be connected directly to the power unit, with the signal wire's voltage decreased by a voltage divider (to around 3,3V). It worked flawlessly for some time, but I actually had some malfunctions that day, like for example manual bed leveling created a mesh with offsets around +7.0 or some other time the values of offsets were correct (or at least believable), but nevertheless nozzle moved very far from the bed. Only unplugging and plugging the cord resolved the issue.

Thank you in advance for your insights.

In general, once the controller board smokes it should be replaced.
With that said, the cause should be investigated and fixed.

There is a thermistor on the hot end whose signal is used by the board to turn on & off the heater for the hot end. A failed thermistor could lead to a constantly on heater (if the firmware does not turn it off). A constantly on heater would cause over heating. Overheating could fail the thermistor. A heater on constantly could burn the controller board due to excess current/heat. A failed control on the board could turn the heater on constantly.

I could surmise that the probe being plugged in and unplugged may have damaged the board due to voltage/current fluctuatiions.

Since the parts mentioned are relatively inexpensive I would suggest carefully rebuilding the hot end with new heater and thermistor, replace the controller board. Then test carefully for stable heating temp control before starting another print.

I also would suggest NOT connecting & disconnecting loads while the board is powered.

I keep spare thermistors and heaters on hand since I have had similar failures. I also always keep one spare controller board ready to install.

One little trick I have developed from trial + error testing is that I always coat the heater with thermal paste inside the heat block to eliminate air gaps & hot spots. I also coat the thermistor with the same thermal paste so it gets the temp changes instantly (again no air gaps)

Edited 1 time(s). Last edit at 11/29/2021 02:05PM by wildone.

i agree with wildon....the board is done....i would also be looking at the power supply as its carrying the electrical load of all the affected components you mentioned. perhaps you were approaching the limit of what it could carry. your heater mosfet is probably fused "on" . After years of running a hotend they will eventually wear out, especially with 12v system because amperages are higher. i have cooked at least a couple after long reliable service on a 12v machine. loose connections at the inputs will also make "high resistance" connections that heat up and use up amps. that will cause spikes and low power at unpredictable places. a new load on the system can expose these weak points. "its a machine so it'll fail".....long reliable use will wear things out.....you should probably replace the board....