3d printer thermistor replacement

May 24, 2016

I was having a problem with my bent rod guides and the guys at craftunique got me all squared away on that end. Unfortunately as soon as I started trying to print, another problem showed up.

Yup, I got the red fatal error on my cb. Apparently these normally have to do with the heater sensor or thermistor. Well, I bought some spares off ebay a while back and wasn't sure if I could find them, but I did, not to mention it's almost midnight. These things always happen in the middle of the night. So I figured I check the thermistor end and check the cable as suggested on the forum. https://craftunique.com/forums/view-thread/365

The cable seems fine so I just push the thermistor back out the top to give myself a bit more slack to work on it. I looked for the parts and since I thought I had everything I needed I just went to work on it and thought I might as well change it. As I was cutting through the heat shrink, one of the legs came off. Apparently it was barely holding on. I'm guessing it's still fine, but since I used it for a while now I figured I might as well change it and test one of the 100k ohm versions I got off ebay. I took out the soldering station and went to work. I unfortunately didn't have any tiny leg heat shrink for them and they didn't come with any so I just re-used the old ones. Man, those things are tiny. I finally got it all back together and here are the pictures. In short, now you can just get the ones all set up for you with the wires and heat shrink on them for a few pennies. So I would recommend just getting those instead of the spares that don't come with anything as you'll have to do a bit more work. It's not impossible, but why go through all that. There were not many choices when I bought mine so there you go.

 Here's what it looked like.

 The ebay spares I got a while back. No heat shrink on the legs which you will need. I sure hope they included these now, or you can just get them all set up already since they cost the same anyway. These are 100K ohms if I remember correctly. I don't know what the original specification is, but this is what was readably available for other printers.

 You will also need some smaller heat shrink. I can't find any metric here, so I used the smallest one I had bought from hobby king a long time ago. 1.5 to 2 mm is what you will need. I think I had the 2 mm. It still felt a tiny bit too big but worked okay still.

 I just used this tool to cut through the old heat shrink.

 Just use the top here as a table. Here's the leg that came off as I tug on the heat shrink. So it was barely holding on the whole time.

 This is a good time to triple check the wires. Mine still seem fine. I also move the whole thing manually across the bed before taking it apart to see if there was a break anywhere else. I found it was on this end.

 Finally soldered the new part.

I then added another piece over the individual red pieces to give it a bit more strength.

 I noticed my temps started normal, then went up to 225, then down to 190 and it was all over the place. And this leak didn't help as the melted filament just started falling off and ruining the part too. So even with the new longer tip ends I still had this leak. So I tighten this up a bit more now and I'm guessing my PTFE piece is just getting a bit old and lose too.

 I then noticed when I took this apart, the thermistor was barely inside the hole.

And here's the part it ruined but I was still testing this out. It's starting to look better but I can't say for sure until I can at least get a print finished. I made sure the thermistor is now farther in and the temp seems stable where it should be. I also used a piece of kapton around the block to make sure that stays put. So aside from now using a .45 mm feeler gauge instead of the .3 mm to level the bed, it seems to work. I'm still not sure why the height changes from leveling it to when you start printing, even if I level this hot or cold, it does the same thing. So this is how I ended up with the .45 mm gauge to level the bed since once you start the tip actually gets closer to the bed. I don't know why, but this works for me now. I'll have to check my fan cables next time I take the printer off the shelf.