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Cant Get Hotbed to Work - Newbie

Posted by nickjdunn 
Cant Get Hotbed to Work - Newbie
April 30, 2017 02:49PM
I'm new to 3d printing and got one for Christmas and finally got it put together and almost finished with all the testing and calibrating but having an issue with the hotbed. When I turn everything on and try to turn the hotbed on it doesn't respond at all. I have checked the 12v power coming out of the RAMPS and there is none to the hotbed. When I measure voltage of the thermoresistor of the hotbed it reads about 5v but in the repetier host software it doesn't show a reading for room temp on the hotbed like it does for the extruder nozzle. I am thinking this means that the thermoresistor isn't working and needs replaced? Before I buy a new hotbed I am hoping someone can help me diagnose the issue before I spend the money for a new one.

Any help is greatly appreciated!
Re: Cant Get Hotbed to Work - Newbie
April 30, 2017 06:36PM
The firmware will not allow you to turn the heated bed on if it can't read a sane bed temperature

So you need to get the bed thermistor sorted first, before you can ascertain anything else.

While not heating swap the hot end thermistor and heated bed thermistor plugs around on the controller, does the hot end keep reading room temperature or does the fault move? Now put it back before you forget.

If the fault moves its is likely you have a dead thermistor or cable, if the hot end keeps reading temperature and the bed does not, it is like you have badly configured firmware
Re: Cant Get Hotbed to Work - Newbie
May 01, 2017 12:37AM
How is the room temperature in relation to the minimum defined in the firmware ?
If less, you can not start the hotbed either, so you must lower that number.
This happens with me sometimes, when freezing in my garage.

If it is not less, there is indeed a problem with reading the thermistor.


Orca V4.4 rebuild to Ramps with Mk8 and E3D, as well as a Rostock Delta Mini and an OLO in backorder :-)
Re: Cant Get Hotbed to Work - Newbie
May 01, 2017 03:00AM
You can't check a thermistor with a voltmeter, you'd need to read the resistance ( ohm ) of the sensor. It should be around 100.000 ohm ( 100k ) at room temp.
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