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Heated bed kit: temperature measured too high

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Hi guys

Yes, I need you help... ;)

I installed an UM heated bed kit and the temperature reading says 38°C at room temperature (btw. the temperature of both hotends also at room temp say 21-23°C). So temperature measurement is wrong.

A quick test with heating to what should be 60°C show something like 45°C (measured with IR thermometer) effectively (yes, the sensor reacts). So it seems to be something like an offset. Resistance of the PT100 directly measured says 108 ohms, which is 23°C.

Something wrong with the add-on PCB? I have to say I had to cut the 3 wire cable for sig/5V/GND between the UM shield and the add-on pcb. The reason is simple: I had my own heated bed before and therefore had to mount a terminal with screws for Temp2. Does someone know what voltage there should be between signal and GND for room temp?

Any help is welcome, especially if this topic has been posted before (did a search with Google and it was negative): then please just post a link...


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Guys... I'm so sorry... this is embarrassing...


It was not the pcb. It was me. Stupid. Arrgh.

The answer is in the OP.

I had my own heated bed. With an NTC. What do you need to change on the UM shield when you have a NTC? Yes, you need to add a 4.7kOhm resistor to R4.


(sorry for shouting)

The additional resistor reduced the analog signal at temp2 and made the firmware believe the temperature is higher due to the negative slope of the add-on pcb.

@neotko: Thanks anyway for the generous offer!

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To make you feel less embarrassed... I was a lot more stupid today :)

Lesson: always unplug you power tools for a tool change....

Don't worry. I'm oke. Just lost the nails, a little flesh, and badly broosed but it's very unpractical atm...


Indeed! That looks serious! Get well soon!

Edited by Guest

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