If my electronics are all PSU powered but they turn on my PSU, how do I turn my printer on?

Sort of a dumb questio but I'm a little confused. I want to hook up my PSU to my RAMPS By plugging green into PS_ON, and then I'm gonna cut out D1 and plug a 5V line from my PSU into the electronics (either the VCC next to the reset board or the barrel plug depending on which one if those work)

But anyways, how would I turn it on then? Do I have to pick one or the other?! I just really want my electronics to be able to kill my PSU in case I blow a mosfet and overheat the bed or something. Thanks.

If you are using an ATX power supply, there is a 5V standby power wire used to power the PC circuitry for turning the computer on via soft switch that solves the catch-22. Don't know whether it is rated to power the entire 5V requirements of your board(s), but it is worth investigating if nobody has a better solution.....

vreihen is right, use the purple 5v standby line. I just did it and it works great.

[forums.reprap.org]

Thanks! Just what I was looking for. Since we're all on the same page would you mind explaining one last detail? So you connect power (purple) to the VCC pin next to the PS_ON and the RESET switch? Will that power the Arduino, after I cut out the Diode? Thanks a ton!

I believe that is right, SamS. I actually spliced the 5v standby line into a USB connector so my Arduino is getting powered through USB (by way of a Raspberry Pi). But reading the RAMPS wiki it sounds like you are on the right track (5v standby to VCC, D1 diode removed).

Quote
RAMPS 1.4 Wiki
The VCC pin can be connected to your ATX's 5Vsb to continuously power the Arduino from your ATX power supply. You will want to make sure that D1 is not installed or cut out. The Arduino is not designed to be powered directly on the VCC rail and the VIN pin at the same time