Issues with Printer Bed on i3 Prusa Hephestos

[Cobra]

Hello

I am having some strange issues with my self built i3 prusa Hephestos:
We used to have an older printer with a heatbed (Mk2A) that we reused for the newly bought i3 prusa hephestos kit.
Now we connected everything to the board according to the manual and configured the firmware properly for it to work.

When we start up Repetier host we see the heatbed connected and also can heat it.
However it seems that always after a certain time the error "Bed sensor error" (or similar, can't remember the exact words) appears in the console and the printer enters dry mode.

Now as we mostly only print with PLA I deactivated the heatbed in the firmware as it caused the printer to stop its print while he was printing.
We checked all the cables for faulty contacts, but as repetier host sees the heatbed for the first few minutes shows me that it is not a faulty connection problem. Also when I just restart Repetier host and reset the printer after the error occours, the heatbed is there and working again for a few minutes until the error appears again.

Does anyone know what could cause this issue?
We are suspecting that we might have broke the heatbed somehow when removing it from the old printer and installing it on the new one.

Firmware used: Repetier firmware 0.92 beta (also occoured with 0.91)

[wenganxiang]

Is the hot bed thermistor fine? Can you get a stable resistance with multimeter?

[Cobra]

Is the hot bed thermistor fine? Can you get a stable resistance with multimeter?

Thanks for the reply.
How do I correctly measure its elelectornic resistance? I haven't used the multimeter on the heatbed.
I still find it strange that it works in the beginning and then stops and works again when I reset the printer.
The bad thing is, that I don't know what thermistor is installed on the heatbed. We bought the heatbed together with an old used 3d printer and moved it to the new printer when we got the new one.

I am close to just buy a new one and see if that one works, those heatbeds are not very expensive.

[wenganxiang]

Thanks for the reply.
How do I correctly measure its elelectornic resistance? I haven't used the multimeter on the heatbed.
I still find it strange that it works in the beginning and then stops and works again when I reset the printer.
The bad thing is, that I don't know what thermistor is installed on the heatbed. We bought the heatbed together with an old used 3d printer and moved it to the new printer when we got the new one.

I am close to just buy a new one and see if that one works, those heatbeds are not very expensive.

You can swap the connection of extruder thermistor with hot bed thermistor. If it displays other error about sensor instead of "bed sensor error", we can conclude the hot bed thermistor is bad.
I use MK2a hot bed with size 20x20cm, its thermistor is 1.2ohm.
There are 2 wires from hot bed (not thermistor wires), use multimeter to check the resistance of 2 ends of wires.
I use Geeetech Prusa i3, so I describe the steps according to my printer type, hope it fits yours too.

[Mjolinor]

If you do not know what thermistor is fitted then how did you pick the right one when configuring your firmware?

Maybe you just have the wrong one selected in configuration.h (assuming it uses Marlin)

[wenganxiang]

If you do not know what thermistor is fitted then how did you pick the right one when configuring your firmware?

Maybe you just have the wrong one selected in configuration.h (assuming it uses Marlin)

You can ask the seller or techique support what thermistor is fitted. Maybe I misunderstood your words at the beginning. It would be better if you describe your problem with some photos or video.