Note: Also had to change the firmware to accept my new hotend operating temp of 220C (max for me is 235 now). They put this thermistor on top of the heating element pretty much.

I would recommend an Azteeg X1 as a sanguinololu equivalent, or X3 as an upgrade, from panucatt.com.  The X1 is better quality than Sanguinololu, supports a gcode  controlled fan directly, and has headers for plugging in a SDRAMPS card reader.

That X3 is pretty. Is the AtMEGA2560 compatible wit the Sanguinololu? I have a spare Sanguinololu that I am going to use as a test board for my bowden setup. However, it doesn't have the ability to attach a second extruder so I will need something with more drivers. The X3 is almost overkill in that department with 8 driver slots! wow!

If you are picking up spares, consider ordering a stepper driver or two.  When I had to send my Azteeg in for replacement after I fried something, I was able to get my Sanguinololu back into service.  When one of the Pololu steppers burned out, I swapped it for one of the drivers I got with the Azteeg.  I started getting Y skipping, and fixed that by replacing its driver as well.

You don't need to completely duplicate the printer, but picking up some spares here and there when you don't need them will make you very happy if you eventually do.  Nozzles, PEEK barrels, and resistors would be at the top of that list.

Good call on the PEEK. I could use one right now.

You don't need to completely duplicate the printer, but picking up some spares here and there when you don't need them will make you very happy if you eventually do.  Nozzles, PEEK barrels, and resistors would be at the top of that list.

I think then it should be a drain-source short circuit of the MOSFET in the hotend drive. Apparently those little buggers do that. If you are lucky, the atmega pin is still ok and you can just replace the mosfet (and the hotend). If you are unlucky, the pin is fried too and you need to replace the chip... Sorry for the bad scenario...

I think you are right about the mosfet. When I plug power into the board the hotend starts heating up with out the extruder heater button selected.

While I wait for my new Mosfet I just switched the one for the heated bed and the hotend. Anything to get me back up and running.

You might have a bad connection to your thermistor- from what I gather if the temp sensor fails mid print, the board will see 3 degrees Celsius and attempt to increase the hot end temp. However I think this was fixed in a firmware update. Are you using Lawsy's firmware or stock?

Yes but that wouldn't explain why he's seeing 320°C in Repetier, and rising... That's a really odd behavior... Unless the thermistor failed and then started working again when it was already too late.