i3 bed temperature running away...so heat, much hot

I'm currently taking an additive manufacturing class and part of the course involves the class assembling the Folgertech Prusa i3 2020 kit. Mine has come together as I'd expect save for one problem.

I seem to have no control over the temperature of the bed. It seems that whenever the printer is plugged into AC power, the bed begins to heat. As soon as I start a print, the bed seems to race up in temperature. I haven't let it get much past 100C and as you can imagine, my PLA prints are not sticking at that temperature.

I'm using Slic3r with Repetier and the temperatures displayed on the "Manual Control" tab seem to be accurate, at least when the bed temperature is skyrocketing, it is reflected on the bed temperature curve.

I've confirmed that I'm using the same firmware as my classmates and none of them is having the same trouble. I've checked my wiring and as far as I can tell, it's wired correctly. I measured the voltage at the power supply and it's simply line voltage. I haven't measured voltage elsewhere but I'm happy to do so.

At one point, I removed the bed thermistor completely and the temperature read 0 degrees but still the bed got so hot that I could not touch it and my prints won't stick.

I've set the bed temperature to 55C in Slic3r and Repetier but neither seems to have any control over the temperature.

So, being new to 3D printing, I"m fresh out of ideas. I've been building tube amps and guitar effects pedals for just shy of ten years. I'm handy with an iron and a multimeter and actually enjoy troubleshooting (you always learn more about a circuit when it doesn't work right the first time). So please tell me where to probe and what to look for.

I'm happy to include voltages and a copy of my configuration.h file if that'll help but it'll have to wait a day because my printer is at school.

Please tell me there is some hope and thanks in advance.

You probably have a dead bed mosfet on the ramps board, these die closed quite often.

Swap the ramps board from another machine and verify it now works.

I've got class this evening so I'll give that a try and report back. Thanks for the reply!

Turns out Folgertech included a bunch of spare parts including an extra RAMPS board so I swapped it out and Voila! I was back in business. Thanks for the reply, I'm sure I'll be back soon with more questions.