I have my p3steel (with ramps1.4) since 3 or 4 years ago, and have always printed with the heatbed at 90C at most, mainly printing abs. A month ago I decided to test printing some abs with the bed at 100C and did a couple prints without any problem, but after that the heatbed struggles to even get past 80-85C.
after reading some post here and in other places, this is what I have done to try to find the culprit: disconnected the printer, and measured with multimeter the resistance between the heatbed pads. it shows 1.2 ohms (if I just touch the multimeter probes together, it shows 0.2, so I guess the real measurement of the heatbed must be around 1ohm?) so I guess the bed is ok.
Then I connected the printer and heated the bed. I measure voltage with one multimeter's probe on the bed + pad, and the other probe on the - input connector on the ramps (the one coming from the power supply), it shows around 12v, BUT if I do the same with the negative probe on the - pad of the heatbed (instead of in the - connector from the power supply), it shows much less, around 6-7V. (also if I measure in the - connector on the ramps (the one going to the bed) it shows the same 6-7v. So apparently the problem is not on the cables).
So with this data... should I blame the mosfet? I have got a new ramps1.4 board and will just replace it, but would like to know your opinions about it...
