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So I just installed a HE280 on my v2 and installed the firmware. However, whenever I switch on the printer, the screen briefly shows something around -2 deg on the hot end then goes to def. Double checked the wiring, and soldering on the accelerometer pcb and it all looks good. Anybody know why the hot end thermistor isn't reading?

Solution:
I replaced the thermistor and completely re did some of the crimp connectors on the rambo and the thing is working again.

There's a wiring issue with the thermistor. Check to make sure that the whip connector is fully seated in the HE280 PCB and that all the pins are fully seated in that connector as well as the connectors on the other end.

g.

geneb wrote: ↑Mon Feb 11, 2019 8:21 am There's a wiring issue with the thermistor. Check to make sure that the whip connector is fully seated in the HE280 PCB and that all the pins are fully seated in that connector as well as the connectors on the other end.

g.

Double checked the wires again and even ran new wires from the pcb to the start of the whip but its still reading def.

There's a wiring issue or the thermistor is bad. You can check the thermistor by measuring its connection point on the PCB with a multimeter. It should read around 100k-ish at room temperature.

g.

geneb wrote: ↑Tue Feb 12, 2019 9:51 am There's a wiring issue or the thermistor is bad. You can check the thermistor by measuring its connection point on the PCB with a multimeter. It should read around 100k-ish at room temperature.

g.

So I measured everything. Across the thermistor wires going to the accelerometer pcb, it read about 14 v at .02 a and no resistance. Across the green and white wires plugged into T0 on the Rambo, it read about 5 v with no current or resistance.

A thermistor is a resistor that changes resistance with temperature. Testing it's condition by measuring voltage going through it is like measuring the diameter of a car tire by checking the internal pressure.

Don't test the thermistor with the RAMBo powered up, or with the thermistor connected to it. If it's connected to the RAMBo, you'll never get a good reading.

g.

geneb wrote: ↑Wed Feb 13, 2019 7:45 am A thermistor is a resistor that changes resistance with temperature. Testing it's condition by measuring voltage going through it is like measuring the diameter of a car tire by checking the internal pressure.

Don't test the thermistor with the RAMBo powered up, or with the thermistor connected to it. If it's connected to the RAMBo, you'll never get a good reading.

g.

Tested the resistor again and it read about .715 k across the thermistor leads.

Tested another glass thermistor i had and it read about 179k. Looks like im replacing a thermistor.

noname117 wrote: ↑Wed Feb 13, 2019 11:40 am

geneb wrote: ↑Wed Feb 13, 2019 7:45 am A thermistor is a resistor that changes resistance with temperature. Testing it's condition by measuring voltage going through it is like measuring the diameter of a car tire by checking the internal pressure.

Don't test the thermistor with the RAMBo powered up, or with the thermistor connected to it. If it's connected to the RAMBo, you'll never get a good reading.

g.

Tested the resistor again and it read about .715 k across the thermistor leads.

Tested another glass thermistor i had and it read about 179k. Looks like im replacing a thermistor.

Wired a new thermistor in but its still reading -3 deg on start up before cutting to def. The thermistor reads about 135 k on the multimeter

You might want to contact support at this point. I don't have any other suggestions, sorry.

g.

Is this the revision with or without the thermal fuse? If it is check that and check that the circuit through the heater is not open circuit.
Also check the resistances from the solder on the board in case of a dry join, the thermistor wires are so small that may be an issue.
Also I ruined a board by pulling the track off of the board during re-soldering so don't be a gorilla like me.

The thermistor is connected in series with another resistor that's sized to make the thermistor run in its "sweet-ish spot" when it's at its working temperature. There's a good chance that this resistor is bad.

That said, one of the things that I would be squeamish about is mucking around with thermistor circuitry. Unless you just absolutely had to have a new house...