So I cannot get any of my 5 hot ends to work. I took all the nozzles off and put new ones on, and then unclogged the tubes. The insulator stayed good. Two are wrecked because the threads stripped out on one and the wire to the heat sensor broke on another.
Now when I go to use my machine none of the hot ends will warm for machine use. I made a video to show what I am doing to test them. Ideas? Suggestions? Help!
Here’s another video.
Its not generally a good idea to unplug and plug electrical stuff when powered up, I’m not saying that that caused the problem.
It looks like the thermistor is connected OK as ypu are getting a sensible reading but there must be an issue with the heater connection or circuit. You could look for damage to the connector on the circuit board side i.e. the wires going into the head unit.
Another tip for the future, if you loosen the grub screw on the bottom of the heater block you can remove the heater tube from the side of the unit, the thermistor just pops out (some use thermal paste when putting it back) then you can drop the nozzle, block and heat break together leaving the heater and thermistor connected.
The threads may have stripped if you didn’t have the heater block at a high enough temperature, makes it a bit trickier to do without burning your fingers (I have scars) but it is the best way.
So my next stupid question, where are the circuits? Do I unscrew the back or the side?
Total newb 
Oops, I’m misleading you - I was just doing the same job but on the Snapmaker Original, you’re right to just unplug the whole thing on SM 2.0. Everything else applies. Sorry!
What I meant was to check to wiring on the socket you plug the hotend into. BTW the circuit board is under the cover on the left but unless something is actually burnt on there there’s not much to see.