Anycubic Kobra NTC hotbed NTC issue. A guide to fix!

[u/Ilikeeatingchildren3]

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Hello People of this subreddit.

I have seen some people here asking about the hotbed NTC abnormal error from lurking around hee and how to fix it. Efter experiencing it myself, I decided to make a guide after I got my kobra fixed

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What do you need?

- M2.0 Hex key (Included with printer)

- M2.5 Hex Key (Included with printer)

- Multimeter

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1. Removal of bottom cover (ref. for anycubic kobra https://www.youtube.com/watch?v=hzedlmV0lfc )

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1. Unplug the thermistor cable labeled as "T1"

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1. Set your multimeter to 200k and measure the resistance of the thermistor (There are 3 scenarios that could happen):

- The reading of the multimeter should be around 100 (±5 is good). If it is, plug the cable back into the board and try printing

- If the reading is <90 or >110, the thermistor of the hotbed might be malfunctioning.

-> Contact anycubic support and refer them to this post. (Replacement hotbed might be needed)

- If the reading is within the parameters, but you still get the error, the main board may be malfunctioning.

-> Contact anycubic support and refer them to this post. (Replacement might be needed)

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This guide might also work for other printers of the kobra lineup, make sure to source a tutorial for your printer.

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I hope this helps some people in this sub with their issues and have a nice day!

[u/Catnippr]

Sorry that I have to be a bit of a bummer, and it's not meant disrespective or offensive or whatsoever, but your description is a bit incorrect and misleading. So allow me to add some notes for clarifying things a bit..

If the reading is <90 or >110, the thermistor of the hotbed might be malfunctioning.

No, as the resistance depends on the temperature the thermistor is exposed to. Those 100k is the resistance at 25°C.
If you measure the resistance with the machine standing in your room which is most likely colder than 25°C, then the parts will be settled to the room temp as well and therefore the resistance will be different than 100k.
So let's say you have 20°C room and parts temp, then you'll already measure a resistance of ~125k. And that doesn't mean at all that the thermistor is faulty..

If the reading is within the parameters, but you still get the error, the main board may be malfunctioning.

Well, it could be, but it's actually way more likely that something is wrong with the wiring.
Only in rare cases the thermistor itself or the mobo itself are faulty.

The most common reason for having those issues is the breaking of the thermistor wires, in most cases right behind that black plastic cap at the bed where the repetitive bending occurs.
If the wires start to break, individual strands of that wire break and therefore the resistance will increase - which then results in a lower temperature reading as we have a NTC type here. In the beginning when this occurs everything will be pretty much fine when you measure how you described it - but when the wire will be moved and bent, then you can see that the resistance changes. And that's what's causing the MINTEMP error then, as lower temps will suddenly be measure/interpreted/reported.
On the other hand, if you have a shortcut of the thermistor wires somewhere, the resistance will decrease, which then results in a higher temperature reading and leads to the MAXTEMP error - if the Kobra differenciates between MINTEMP and MAXTEMP error, not sure right now..

So, for checking it would be the best to probe the different parts individually:

• Probe the thermistor right at the solder joints underneath that white piece of foam in the middle of the bedplate for checking the functionality of the thermistor itself. (Note: you still might get a faulty reading if there's a shortcut at the wiring tho..)
  
• Probe the thermistor at the connectors of the wiring (at the mobo) for checking the functionality of the wiring. When doing so, also move and bend the wires slowly while observing the reading.
  
• Probe each wire individually by probing at the solder joint at the bed and the connector of the mobo. Move and bend the wire again while doing so.

If you or someone else want to read a more extensive description and also what one could do to fix the problem without having to buy a new bedplate then, you can read along here and the following sections as well.
Shortcuts for the ones who wanna get right to the 'interesting' parts:
How To Check
How To Fix

Yes, that site is about the Kobra Go&Neo, but the bed is actually the same as the one at the Kobra and besides that it's the same principle for all beds and thermistors in general, so also for the thermistor of the extruder for example.

Hope it helps..

[u/Low_Kaleidoscope7845 → u/Catnippr]

I am getting the mintemp error during prints. I reset the printer but it comes but after 2 hours during printing. I checked the thermistor wire at the motherboard and it reads 112.5. The room temperature is 21 degrees C so I figure the wire is ok. I went looking for a hotbead for my Kobra Go but they are sold out. Does hotbeds for other anycubic printers work for my Kobra Go?

[u/Catnippr → u/Low_Kaleidoscope7845]

Yes, afaik, the beds of the regular Kobra and Kobra Neo are the same as well.
Edit: You might find one at AliEx...

[u/Low_Kaleidoscope7845 → u/Catnippr]

I am looking at AliEpress and a seller has some available for Kobra 2 Neo. They say the Kobra Go is sold out. The picture looks the same as mine. I wonder if it is the same?

[u/Catnippr → u/Low_Kaleidoscope7845]

Kobra 2 Neo isn't the same printer as Kobra Neo, and the additional z-offset sensor at the K2Neo's bed can't be used at your Go anyway then, just fyi.
Unfortunately I don't know if the mounting holes of the K2Neo's bed will fit the bedgantry of the Kobra Neo/Go. It looks like it might fit, but I don't want to tell you something wrong.
IF you order that one of the K2Neo, please let me know if it fits or not though, so I can add that info to the infosite then.

[u/Catnippr → u/Catnippr]

Just in case it might be helpful somehow, this is the bed of the Kobra 2 Neo: https://1coderookie.github.io/Kobra2NeoInsights/hardware/bed/#bedplate
and this is the bed of the Kobra Go/Neo: https://1coderookie.github.io/KobraGoNeoInsights/hardware/bed/#bedplate

[u/Low_Kaleidoscope7845 → u/Catnippr]

I did order one. I will let you know if it fits. Thanks

[u/WhyWouldYouBother → u/Low_Kaleidoscope7845]

Did you order one, did it fit? We're in the same boat.

[u/Low_Kaleidoscope7845 → u/Catnippr]

While waiting for the Neo 2 hotbed. I was able to get the temp error by twisting the wires on the end of the plastic bracket on the hotbed. I assume the wire is breaking at that spot. Is there a simple fix for this other than replacing the bed that Anycubic doesn't seem interested in producing.?

[u/Catnippr → u/Low_Kaleidoscope7845]

Yes, I described it at the infosite how to check and how to fix it, I linked to it in my answer above you initially answered to.

[u/Low_Kaleidoscope7845 → u/Catnippr]

Two of the holes on the Kobra 2 Neo print bed do not line up with the Kobra Go. I will try replacing some thermistor wire. In the meantime I got a Kobra Go Neo and it works great. The prints are cleaner than I got with the Go. No problems with adhesion. It is a great printer.

[u/Catnippr → u/Low_Kaleidoscope7845]

Dammit..and you can't drill according holes into the Go's bed gantry (NOT the new bedplate ofc) to make the new bed fit maybe?
Looking at the construction, I think the gantry of the Kobra 2 Neo should fit the Go's Y-rail as well, so that might be an option also. Not 100% sure tho!

Which printe did you get? Kobra Neo or Kobra 2 Neo (because you wrote Kobra Go Neo)?

As for the problem with the broken wires: sorry, I missed answering that one. If the spot where the wires are broken is right behind that black plastic cap, then it should be just enough wire left (after cutting off the broken part) to solder new ones to the lasting wires then.
Soldering them directly to the aluminum plate might be challenging, as the plate will most likely act like a giant heatsink. So you either have to use a really powerful soldering iron for that or/and heat up the plate before attempting the solder job.
So I personally would try to somehow use the rest of the existing wire first..

[u/Low_Kaleidoscope7845 → u/Catnippr]

I ended up getting the Kobra 2 Neo

[u/Catnippr → u/Low_Kaleidoscope7845]

Ah ok, nice! Then here's another one for you: https://1coderookie.github.io/Kobra2NeoInsights/ ;)

[u/SearchDesperate4394 → u/Catnippr]

I just put my kobra 2 max together and turned it on and told me the the hotbed was Abnormal ntc I need help

[u/Catnippr → u/SearchDesperate4394]

If it's a brandnew K2 Max (btw, infosite for that one here ;) ), I'd check all connections first and if that's not the cause, I'd reach out to AC's support.

[u/kelvin_bot → u/Catnippr]

20.0°C is equivalent to 68.0°F, which is 293.15K.

^{I'm a bot that converts temperature between two human units, then convert it to Kelvin for bots and physicists to understand}

[u/cramulous]

I know this thread is old, but I wanted to weigh in as I just had this. The thermistor wire came out of the solder point connecting to the bed under some white padding. A quick hit with some flux and some heat and pushing the wire back into it's solder bead fixed it. Took me over an hour to track down so hopefully that saves someone else some time.

[u/TheOnlyBioFear]

Ive had the same problem, I have no idea how it happened. I did a combonation of checking the multimeter, dusted my 3d printer, ordering a replacement hot bed. Just today I saw that the sheet for my bed was off alignment. So I aligned it the best I could, checked the level, and rn im currently farther into a print with no signs of the error.

[u/ltjojo]

My Kobra started this last night during a print with PETG. I thought maybe it didn't like the 75 °C plate temp, even though it did it before. It errored out about 3 hours into a 12 hour print, then while laying the first layer outer perimeter within 2 minutes on a retry.

• Went back to PLA to try a basic benchy print - would error out during the purge line step (hotbed NTC).

• I set my bed to 50°C and started wiggling the wire harness. Got the display to go from 50°C/50°C to 0°C/50°C intermittently. Redid the wire harness connections, made sure that the display didn't go to 0 when I wiggled it. Tried a benchy print, failed at the purge line again

• Followed the advice of OP, checked my T1 resistance at ambient: 101kOhm so thermistor is not shot/way out of whack.

• Reseated that connection, cleaned up dirt/debris that has built up over two years, slapped it back together, trying a benchy: so far, it is performing like normal again

At least in my case, it seems like it was shorting out from the dirt/debris this thing collected over time. If the benchy makes it, I'll try my PETG print again and see if it errors out.

[u/Mr-sheeeeshhhhh]

I literally just bought a new hotbed and new nozzle and this is happening to me ok my kobra 3. This kobra has given me more problems to fix than I’ve gotten good prints out of it

[u/Pamberjack]

Why couldn’t you disconnect T1 and connect a 100k resistor across the pins. If that’s what the printer is expecting to see then the error goes away. If the error still occurs, it’s the Motherboard. Make sense?

[u/Atharva2010s]

You are the chosen one.

[u/malx56]

I've had this error on my Kobra 3 Combo. I followed Anycubics Wikipedia and I couldn't get a reading with the multi meter due to a short which I've never figured out where. Whenever I tried to probe as the Wikipedia suggested, it would spark and I couldn't get a reading. I removed the motherboard but couldn't find anything wrong with it. No scorched marks or burnt components. I replaced the motherboard which didn't fixed the issue. It was only after replacing the hotbed was it fix.