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I have a Rostock Max V1(FEB2014) with some new v2 parts. I recently removed my e3dv5 head and installed the stock one since i believed the nozzle was bad. I get the stock head installed the run it to temp to calibrate it then I notice the temp was really high and the peek was melting in half. I shut it down the proceded to order replacement parts. I ordered an e3d knock off just to try it out since it had decent reviews. I installed it tonight then ran the PID auto tune and was watching it closely when I noticed the temp keeps climbing past the 200 mark. It wont shut off power to the extruder except by a hard reset. I tried clearing EEPOMS and reflashing firmware, and I even bought Simply 3d to see if it was MatterControl since it was suggested on a forum. The only shot in the dark I have is that a MOSFET crapped out on me. I really don't want to have to spend another $200 for a RAMBo on this printer for a hunch. Any Ideas or suggestions?

I imagine if the mosfet had failed, it would be heating the whole time the supply is on, is that what's happening? Sounds like its only heating too much when your actually requesting heating?

I also doubt it's the RAMBO, if you can turn the IO pin on, it can be turned off, and I've never heard of a mosfet failing such that it was off at power up, but always on after being turned on.
Make sure you the the heater plugged into the correct output on the RAMBO, if it's plugged into the second extruder port, it will turn on and stay on until the temperature drops below 50C (which of course it never will).
I assume it was working before you replaced the E3D?
It could be some external wiring fault, but I'm at something of a loss to understand what exactly.

You could connect a fan or LED to the MOSFET, and that would give you a tool to diagnose with. watch that, and let us know what happens when you "print" with the LED

Thank you for all the replies. When I switched to the stock head I added a xt60 connector for easy swapping. I kept my pairs correct but I hooked them up to the wrong set on my 18-4 extruder wire pairs. I was hooked into extruder 1 instead of extruder 0. I didn't even check before because I haven't touched a screw on the RAMBo in almost 2 years. Again thank you all for the help. Should I post the pictures of the melted PEEK?

Yeah!

We love that kind of stuff!

Now that is what I call melted Peek!
Suitable for framing!