Rostock Max V3 - hot end heater always on

[theDaemon]

I have a new Rostock Max V3, DIY kit. About a week old, roughly 30 hours of print time on it. Followed the online instructions to the letter, and as a V2 owner, feel like I got it right. It ran great on the first print after calibration, using the 12/09/2016 firmware, which appears to still be the latest.

I was in the middle of a 16 hour PLA print, when I noticed a burning smell. I went to inspect the print, and found charred bits of PLA on the print itself and around the nozzle, as well as the PLA at the nozzle exit smoking. The LCD display showed a steady bed temp, but the hot end heater oscillated between my set temp (212*) and about 136*....back and forth and back and forth. Neither was even close. Infrared thermometer on the heater showed it was way, way, way overheating. On the LCD I turned off the heaters "Turn off all Heaters" menu option, but the hot end heater stayed on, as did the red LED on the HE280. I went to the Set Temp menu and set it to 0 - the hot end heater stayed on as did the red LED on the HE280. I killed the power to the machine and put a fan on the hot end to try and prevent a full-blown meltdown. The runaway resistor did not appear to kick in, it just heated itself into a near fire.

Henceforth, every time I power the unit on, the red LED on the HE280 turns on - even not having touched the controls - and the heater goes to town full blast. Reset the RAMBO - same problem. Re-flashed the latest firmware directly from GitHub (which is the same version I already had) - same problem. Reseated the whip connector - doesn't make any difference, it heats out of control when connected. I see nothing visible with the RAMBO (all wires still attached, etc.) HE280 thermistor reads ~100k as it should. Clearly I am getting tons of power to the hot end because it heats in a runaway fashion.

Running short on ideas of what to check here, and a search of the forum did not yield any clues.

Anyone seen something like this before?

[czecht]

Have you find a solution for this problem? I'm looking how to fix the RED LED on RAMBO also.