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enter image description here

Hotend drops from 205 °C to 175 °C, and then the printer errors MINTEMP. How can I fix this? Fan is not starting yet.

#define  DEFAULT_Kp 28.65
#define  DEFAULT_Ki 2.80
#define  DEFAULT_Kd 73.33

#define HEATER_0_MINTEMP 5

MINTEMP is 5 °C? It's impossible it's getting that cold.

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  • $\begingroup$ Is your fan coming on? Do you have an M106 in your gcode? $\endgroup$ – Davo Sep 9 '19 at 19:45
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    $\begingroup$ Your hotend thermistor is reporting -27 ºC considering the bed of 27 ºC (so your ambient is about 27 ºC) there must be something seriously wrong, possibly the thermistor. $\endgroup$ – 0scar Sep 10 '19 at 6:43
  • $\begingroup$ @0scar the dropping spikes tell the story of disconnecting the sensor... $\endgroup$ – Trish Sep 10 '19 at 9:00
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    $\begingroup$ @Trish Excatly, something seriously wrong. You see the ambient temperature being (very shortly) reported correctly at about -10 minutes in the graph, so this must be a connection issue or faulty sensor. $\endgroup$ – 0scar Sep 10 '19 at 9:36
  • $\begingroup$ Yes this is a connection issue, some wire can be loose or internally broken. If the sensed temp is negative the thermistor is damaged or a broken end terminal. This error is normal when your wires are not well routed and protected or too tight. $\endgroup$ – Fernando Baltazar Sep 10 '19 at 18:16
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Sudden drops in temperature curves like in your picture are usually missing readings on the thermosensor:

Disconnecting the sensor from the board registers as min-temp of the sensor while shorting out as max-temp, so it triggers the mintemp/maxtemp security protocol: shutdown.

One could disable mintemp/maxtemp protection, but that wouldn't solve the issue. The issue is usually the wiring of the sensor. To find the fault, put temperature on the sensor but keep the motors disabled. Watch the read temperature. Move the printhead manually and slowly. If it suddenly drops and throws the error, you might have a faulty lead close to the printhead. If not, you need to open the electronics box to check if the connection to the board is ok. In the worst case, you might need to exchange the whole temperature sensor.

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