Welcome to the SeeMeCNC Community

Hi,

Been searching a lot of the forums before posting and it seems other people have similar errors to mine but most of these errors are occurring for folks after they've printed a few prints.

I just turned my printer on for the first time, and am up to Step 6: Calibrating, but I'm having errors from what I think are the thermistor(s).

When I start the printer up, NOZ: def and BED: def show up after flashing at 5.1 and 23 respectively.

I'm pretty sure the BED thermistor is reading accurately, but when I hit "preheat" in the controls of MatterControl nothing happens. When should the LED on the bed be on? From when I turn on the printer or after I activate it in MatterControl?

Then, the hot end thermistor is clearly not reading correctly. When I hit "preheat" in the controls of MatterControl, the "Target" box goes from 0 to 215 C, so at least something seems to be happening, but the hot end doesn't heat up. I've already broken two thermistors, so I'm pretty terrified to mess with the thermistor anymore on the hot end. I checked the solder and it looks pretty good. I also made sure neither of the two wires are touching anywhere. Is it possible to have soldered it backwards (power and ground)?

Possibly relevant information: Both thermistor temperatures are fluctuating +/- one tenth of a degree, so that gives me hope that they are working? Also, I am in southern california and the temperature in the room the printer is in is DEFINITELY greater than 18 C. When I turn the "Fan" on in MatterControl the 3 side fans all turn on and the pink LED on the Hot End lights up. Also all of the commands in the "movement" category work fine. MatterControl keeps telling me the printer is set into dry run mode until restart.

Obviously I'm completely inexperienced in all of this, but any help would be greatly appreciated. I'm hoping I can at least fix the bed issues and maybe purchase a pre-assembled hot end if mine is too messed up.

Thank you!

-Matthew

It is likely that you have a bad joint somewhere adding resistance, and making it think it's a lower temperature (As the thermistors are Negative temperature co-efficient, AKA they get less resistive as they get warmer). I would check your connections all along the signal path. However, a thermistor is a fully passive and unpolarized component, so it is impossible to have backwards.

As soon as the nozzle thermistor registers that low, the printer assumes a hardware failure and refuse to heat, so that's normal. I'm going to figure that it's only one problem, and that it's likely bad contact or a cold solder joint somewhere.

I checked the following connections:

Where the thermistor is soldered to the accelerometer board, looks good. I unscrewed the board to see if maybe it was pinching it too, no change.

Took off the heatshrink at the end of the wire whip to make sure it didn't pull the green or white wires out. Pushed them all in with a pair of tweezers just to make sure. no change

Unplugged and replugged the T0 connector to the rambo, no change

Any other locations I should check? I don't have a multimeter unfortunately so I can't check each individual step.

Also unscrewed the screw at the nozzle tip securing the thermistor in place to see if that was pinching or causing contact, no change.

Having the same issue. Checked and double checked the thermistors.

I had the same issue when the big plug on the hotend wasn't plugged in correctly. but I assume you already checked it

I replaced the thermistor on the hotend without any change to the startup temp readout. I also bought a multimeter to try and get to the bottom of this but I'm stumped. I tested the resistance of the thermistor with a readout of 1.5 (I'm not sure what units it is using- the multimeter i bought is autoranging), and then I also tested a brand spanking new thermistor that literally had never been touched and that was returning 1.3. Then, while keeping the leads of the multimeter touching the hotend thermistor I put my thumb on the little glass bead and watched the readout go from 1.5 slowly to about 1.1, which to me seems to mean the thing is working. Also, I did the beeping continuity test on the green and white wires of the wire whip and got a solid uninterrupted beeping. I have no idea what to do next. Anyone have any thoughts or breakthroughs with this problem?

It took me a while to troubleshoot my thermistors, but I did eventually manage, so there's hope. Here are some tests I found useful:

1. Swap where the hot end and bed thermistors are plugged into the board, this won't solve the problem, but you should see the 5.1 on the bed instead of the hot end field on the LCD, which tells you that the problem isn't with your Rambo board.

2. Temporarily detach the offending thermistor from the board, and replace it with a 100 kilo ohlm resistor. With this resistor in place, the temperature reading should be within a degree of 25. It is important that you don't try to heat up the hotend when you have it in this state, as you are not actually measuring a temperature.
With the resistor in place:
If the temperature reading is close to 25 then you have a problem with your thermistor, replace it.

If not you have a problem with your wiring; take off the resistor, and unplug the thermistor leads from your Rambo board and use your multimeter to make sure that you have good connections, and that you have no shorts between the wires, or shorts to ground.


Good luck

I have the same problem.
I think it is firmware issue because the NOZ and BED reading was working correctly before I update the firmware.

1. Double check the wiring in your whip connector and on the connectors going into the rambo. Specifically, check the order of the green and white wires. If the thermister wires are backwards, it's going to cause problems. Also, is the heatsink fan coming on when you turn on the machine? When it's powered on, the heatsink fan should be running and you should have 2 blue LEDs showing through the cover on the hot end. Is this the case?

I solved my def issue, I used a multimeter to test the hotend's thermistor, and I found that the thermistor does not work. then I connected the Rombo T0 port to an old thermistor I have and it worked, and the def issue resolved.