Acetone will not dissolve PLA, there are other nasty solvents that do that, but it is not recommended to go that way.

You could apply 12 V (if the cartridge is 12 V that is) directly. As the thermistor does not work, you cannot use the printer board. You should take caution not to heat it too far or too hot, but from your experience with your own machine you should know approximately how long it takes to heat up the hotend to working temperature. E.g. start with a minute and try to pry off the lump of plastic with pliers. If you can reach the bolt/worm screw, try heating until you are able to insert the hex key or screw driver.

This video from Josef Prusa shows exactly what you need to do what is described above. The only difference is that you need to connect the heater element directly to the power supply as your thermistor is broken.

Acetone will not dissolve PLA, there are other nasty solvents that do that, but it is not recommended to go that way.

You could apply 12 V (if the cartridge is 12 V that is) directly. As the thermistor does not work, you cannot use the printer board. You should take caution not to heat it too far or too hot, but from your experience with your own machine you should know approximately how long it takes to heat up the hotend to working temperature. E.g. start with a minute and try to pry off the lump of plastic with pliers. If you can reach the bolt/worm screw, try heating until you are able to insert the hex key or screw driver.

This video from Josef Prusa shows exactly what you need to do what is described above. The only difference is that you need to connect the heater element directly to the power supply as your thermistor is broken. So don't leave it on too long or you will bake the filament to carbonization, which is much harder to remove. Try to cycle it on/off.

Acetone will not dissolve PLA, there are other nasty solvents that do that, but it is not recommended to go that way.

You could apply 12 V (if the cartridge is 12 V that is) directly. As the thermistor does not work, you cannot use the printer board. You should take caution not to heat it too far or too hot, but from your experience with your own machine you should know approximately how long it takes to heat up the hotend to working temperature. E.g. start with a minute and try to pry off the lump of plastic with pliers. If you can reach the bolt/worm screw, try heating until you are able to insert the hex key or screw driver.

Acetone will not dissolve PLA, there are other nasty solvents that do that, but it is not recommended to go that way.

You could apply 12 V (if the cartridge is 12 V that is) directly. As the thermistor does not work, you cannot use the printer board. You should take caution not to heat it too far or too hot, but from your experience with your own machine you should know approximately how long it takes to heat up the hotend to working temperature. E.g. start with a minute and try to pry off the lump of plastic with pliers. If you can reach the bolt/worm screw, try heating until you are able to insert the hex key or screw driver.

This video from Josef Prusa shows exactly what you need to do what is described above. The only difference is that you need to connect the heater element directly to the power supply as your thermistor is broken.