Bed heating error
On first starting up from cold, the bed gets to 30 deg C, and I get a "Err: MINTEMP BED" heating error and the Bed heating turns off. Have to turn off/On the start again and the Bed heats up ok and prints ok.
Firmware is 3.9.3-3556
Is this a hardware or firmware issue?
If the ambient temperature is above 15C, then
Mintemp Bed, is typically a sensor failure, the most common causes are:
Degenerating wires between the bed and the rambo case, (Probably right behind the Y axis Xable Clamp) the continuous flexing of the cables, causes metal fatigue and the connections go intermittent.
Loose connector on the rambo board
Loose terminal in the plug housing at the Rambo end.
another possibility is that the wires for the thermistor have been working their way into the cable strain relief, and have stretched the wires to the thermistor under the bed... at best this can pull the thermistor out from under the adhesive tapes under the heatbed... this would normally cause a thermal runaway, which you are not reporting....
Worst case, it can break the wires to the thermistor which may give the intermittent problems you report.
the thermistor should measure about 126Kohms at normal room temperature 20C and 100Kohms at 25C