Nozzle Not Heating

[FDM_Process]

We just finished replacing the thermistor and heating elements. We are getting a reading on our nozzle temp but it's not heating up. What could the problem be?

[FDM_Process]

Upon further inspection I think there is something wrong with the heating resistors. When I touch them they are could to the touch and it should be burning my fingers. I'm guessing there is a wiring issue somewhere but I am not 100% positive where these are wired to. I've replaced both of the white 5A fuses as well and still nothing is happening.

[Polygonhell]

The easy way to determine where the issue is to use a meter.
Disconnect the heater from the board.
Measure the voltage at the output from the board when it's supposed to be heating, this will tell you if the board is supplying power.
Test the resistance across the terminals, it should be in the 3-4 ohm region.

My guess without any more data is you have an OC or a short in the hotend wiring, but the above should identify where to look.

[FDM_Process]

I have never done this before, what setting should my meter be on?

[FDM_Process]

The board is supplying power. I also disconnected the the wires from the resistor and measured the resistance, it was reading at about 7, but I'm not sure I am doing that part right because I just replaced the resistors so there shouldn't be an issue there.

[KAS]

What was the purpose of replacing the hotend resistor initially?

[FDM_Process]

I'm not 100% positive since I wasn't here, but I was told they went bad. When I got here they were loose in the RTV and when I took them out there were gouges in the coating. I re-routed all the connections from the resistor and even to the RAMBO just to make sure they are all connected right. I even went as far as to take out the wires from the power supply and reconnect them just to make sure everything is making a connection. New fuses and everything in there. The Heated Bed is working, I just can't seem to get the nozzle to heat. Pretty much at a loss here as to what the problem could be.

[KAS]

Gotcha, just trying to get an idea if it wasn't heating before the replacement.

Just to clarify, you do get voltage from the pins directly off the RAMBo on Extruder 0/Heat 0?

Can you take voltage readings from the wires near the hotend when it should be heating the element? ( trying to check for breaks in wire along the way)




[img]http://reprap.org/mediawiki/images/b/ba ... n-main.jpg[/img]

[FDM_Process]

I'm not very familiar with multimeters so I'm not sure if I have it on the right setting. I'm getting a reading of @12 on both ends when I have it dialed on the 20 of the VDC of multimeter.

[KAS]

presumably your software, rambo, and wiring appear to be correct if your getting 12 volts to the wires near your hot end. Only thing I can think of is the resistor itself.

With your meter set to Ohms ( or resistance ) what reading do you get when measuring across both wires of the heating resistor? ( has to be disconnected for proper reading)



A digital Multimeter tutorial that might help : https://www.youtube.com/watch?v=bF3OyQ3HwfU

[FDM_Process]

I'm getting a reading of 7.

[KAS]

Wow, so everything appears to be working accept the getting hot byproduct we're looking for...


Any chance the resistor leads are/were touching metal causing a short? I'd expect that to blow fuses, but you never know.

[KAS]

Set your meter on continuity and test the black wire near the rambo and the wire near the hotend. Do the same for the red near the rambo and the hot end. Let's make sure we're messing with the same set of wires. ( should hear a beep of some sort)

You can test it by touching the multimeter leads together.

[FDM_Process]

Yeah, it's making some noises on both sets of wires on both ends.

[KAS]

ok last thing I can think of. Can you post a picture of your hotend?

[KAS]

Just thinking out-loud. If you have the stock 6.8Ohm resistors and your coming up with 7 Ohms, you might be wired incorrectly

[FDM_Process]

Do you want me to reassemble it and post a picture? I've got everything disconnect at the moment.

[KAS]

nah, just make sure it looks like the examples on page 150/151 in regards to the location of the thermistor and how the two resistors bend and clamp together. Make sure the resistor leads bend on the "flat sections" of the hot end.


I cant see any other reason why it shouldn't work.

[FDM_Process]

Shit!!! Thank you for this, I did have them wired incorrectly. Wow!! I can't believed I missed this!

[teoman]

Max or orion? Did you build it?

[KAS]

Awesome! now you should get that 3-4 Ohm range Polygonhell was talking about above. The resistance value drops when wired in parallel.

Should be up and running in no time!