Think this is now solved.. I didn't have any load on the 5V rail. The ATX monitors it and shuts down if no load . Now stuck a 12V, 20W halogen on that rail so it lights up and I can see visually.. Sometimes just asking the question helps in providing the solution.. Cheers Willby willinilli - Reprappers
It is 500 W Eagle Voltas.. It heats up the bed when directly connected, i.e. not going through the RAMPS.. Have now tried it with a lower bed temperature aim ie 30 oC but it still trips the power..by willinilli - Reprappers
So have Prusa mendel.. RAMPS 1.4 Arduino... Mk 1 Prusa heat bed.. Whenever I set temperature through pronterface, (either by mac or linux), the atx power supply stops.. ie fan stops everything stops... The wires going to the heatbed come out of D8.. the 11A going in to shield as normal.. ( Have checked polarity etc..) Prior to it stopping red LED behind mosfet lights up.. No LED on heatbed atby willinilli - Reprappers