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Extruder Overheating without Command

Posted by cankurall 
Extruder Overheating without Command
May 24, 2020 07:12AM
Hello there,
I am using the Tevo Tarantula i3 model.
My machine stopped suddenly when I last printed. To run it again, I removed the power connector from the motherboard and re-inserted it. My machine, motors, heater bed, fans etc. all of them work, but the extruder automatically goes up to +275 degrees even though I don't give any command. I turn off the device by unplugging it to prevent a fire as it does not happen in any way. I tried it with 3 different extruders and heaters. All 3 of them start to heat as soon as plugging in the device and goes up to max temperature.

Is my problem caused by the motherboard?
If my problem is caused by the motherboard, can you recommend the most affordable model that I can buy and does not require extra fasteners?

The printer I use: [i.hizliresim.com]
Motherboard on: [i.hizliresim.com]
Re: Extruder Overheating without Command
June 05, 2020 12:42PM
OK, there's a possibility that you have a motherboard problem but before spending a load of money, can you check the hot end thermistor? I don't have the same printer as you (I have a GeeeTech Prusa i3 Pro cool smiley where I had problems with the hot bed. The temperature on switch on should display the ambient temperature of both the hot end and the hot bed plus the default temperatures you've set when heated up

Example: Hot End 17/200 Hot Bed: 17/65

Pictures of the Tevo look like the display is common to most i3 printers. What does your printer display on power up?

Disconnect the hot end thermistor at the motherboard (With the power off!) and power up again, the hot end should say 0/200 or equivalent. Can you use a continuity meter (Multimeter on Ohms setting) and measure the resistance of the thermistor when disconnected, I think it should be something like 130Kohms?
My problem was due to a broken wire in the cable to the printhead so I got a disconnected 0/65 display. The hot end works the same way as the bed. I reckon if the thermistor or cabling is shorted out it'll force the heater to stay on as it's unable to regulate.

You said you'd changed the extruder, did this include the thermistor or was it just the extruder and heater assembly? If you changed the heater AND associated thermistor then the board may be the next thing to investigate.

Play Bonny!

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