Heatbed Problem (2 replies)

Hi,

I use Ramps 1.4 with Marlin v1.
When i turn on the heatbed, it heats up for a while but randomly just stops heating. No error for maxtemp or something, it's just stops and the led on the Ramps goes off
I tried it with 3 different Ramps, 2 heatbed's and 3 different thermistors but the effect is always the same.
Heats up between 50 - 70 , led goes off and heatbed cools down slowly, i check the voltage output on D8 and it;s 0

Thanks