Welcome to the SeeMeCNC Community

So when I turn on my Rostock it's reporting the nozzle temp. at -50°. It then reports "def" for temp. sensors.

After turning printer off,

If I stick a 100K resistor in the hot end whip between the thermistor terminals it reports 26°. So that's normal. Also FYI, with whip simply unplugged nozzle reads 13°.

If I measure resistance at thermistor pins or solder points on hot end PCB, it measures appropriately for temp and responds to heat as expected (cross referencing chart). So that seems normal.

But if I plug the whip into hot HE280 plug it reads -50°. What's going on? I'm stumped.

Is this on a printer that was working and it suddenly started doing this, or is this a problem you encountered on the way to getting your printer working for the first time? When it's plugged in to the hot end and you power the machine on, does the fan on the hot end spin up? Is there a blue LED on the hot end?

It sounds like your whip is not wired correctly. Double check the wiring at both ends. It sounds like the thermister is going through a closed loop and that's what is causing the temperature reading to go so nuts.

Take a look at your wiring. If it all looks right, please answer the questions above and post a picture of the whip wiring and the rambo showing which wires are plugged in where.

Ok thanks, dug a little deeper found those closed loops in hot end. One thermistor lead and both leads going to heat cartridge are all closed (all have continuity). So gonna try n' see if I can diagnose this any further.

Ok, fixed. Guess a wire was getting pinched after nozzle hit build plate. Just unassembling fixed. Stayed fixed after reassemble so good to go.

Thanx for the help