Going for heatbed error bingo  

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paulhostettler
(@paulhostettler)
Eminent Member

So I recently installed a new thermistor a few days ago on my Mk3S. Since then, I've gotten thermal imperfections popping up in the print, then a couple of maxtemp errors, and finally this morning I get nothing but bed preheat errors.

I tried the hairdryer blow test on the bed and the temperature detection did go up degree by degree. After a few minutes it had risen from like 24 to 40, and that was on a hot blow, is that enough?

Everything looked A-OK plugged into the circuit board... not sure what to do next. Thanks.

Posted : 31/10/2020 2:38 pm
karl-herbert
(@karl-herbert)
Illustrious Member
Posted by: @cerebratemako

So I recently installed a new thermistor a few days ago on my Mk3S. Since then, I've gotten thermal imperfections popping up in the print, then a couple of maxtemp errors, and finally this morning I get nothing but bed preheat errors.

I tried the hairdryer blow test on the bed and the temperature detection did go up degree by degree. After a few minutes it had risen from like 24 to 40, and that was on a hot blow, is that enough?

Everything looked A-OK plugged into the circuit board... not sure what to do next. Thanks.

I would check all cables to the printing bed and also the plug contacts for breaks or corrosion. The thermistor seems to work.
The best way to check it is with a multimeter.
Thermistor resistance = about 100kohms at 25 degrees C. room temperature.
Heating bed internal resistance should be around 4.4ohms.

https://help.prusa3d.com/en/article/heatbed-not-heating-up-properly_2086

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 31/10/2020 3:42 pm
paulhostettler
(@paulhostettler)
Eminent Member

@karl-herbert

Alright, not exactly sure how to use a multimeter... might have blown a circuit, the red light was on, then I touched the posts while it was plugged it, and it sparked, snapped, and the light went out >.> Light comes back on briefly when I plug it back in, so hopefully just a tripped breaker? I have no idea what I'm doing.

Anywho, moved my multimeter to the omega looking sign portion of the dial, onto 2k (as opposed to 2M, 200K, or 20k). Hopefully that's where it's supposed to be.

The thermistor resistance reading was 97.6k. The reading on the bed, both on the plugs and at the soldered end on the board, was .002k.

Posted : 07/11/2020 3:47 am
paulhostettler
(@paulhostettler)
Eminent Member

So I completely unscrewed the posts then rescrewed them on. Was able to get the bed to heat up to 40 degrees. Thought I'd fixed the problem, closed everything up, but by the time I got it back to my print station, it was no longer heating up. 

The red LED on the print bed connection point briefly flashed, but now it's dark...

Fiddled around with the wiring, the light would occasionally flash on, took a mouch closer look under the wire... a break in the plastic! Damage wire...

This post was modified 5 months ago by paulhostettler
Posted : 07/11/2020 4:21 am
paulhostettler
(@paulhostettler)
Eminent Member

Cut the damaged wire, spliced it with some doorbell wire. Bed heater light stays on now! Heats up to 60 just fine. Started a print, we'll see if it prints the whole thing.

Posted : 07/11/2020 5:17 am
paulhostettler
(@paulhostettler)
Eminent Member

Aaaaaand bed thermal runaway, FML

Posted : 07/11/2020 5:35 am
paulhostettler
(@paulhostettler)
Eminent Member

Apparently the other wire sheared off....

might need to invest in a new heatbed power cable...

The cable in the parts shop is only for removable, while mine is soldered straight into the board. Anyone know where I can order a replacement wire that you solder?

Posted : 07/11/2020 5:53 am
JoanTabb
(@joantabb)
Moderator

I use Flexible Silicone insulated wire for the heatbed power
this has far more cores in the wire than the standard wire, which will make it more flexible and less likely to fatigue due to constant motion...

I don't know where in the world you are, so I have used Ebay, for example... 

the key words are 'Flexible Silicone insulated wire'

by comparison, the Prusa wire has only about 30 cores per conductor. 

You will need a robust soldering iron with a large tip, to solder to the heatbed.   
while removing the old wires, you will find it beneficial to add some fresh flux cored solder tot he joint, to encourage heat transfer and get the old solder flowing.

I suggest that you wipe the old solder off the heatbed pads before attaching the new wires.
 Tin the end of the wire, before trying to solder it to the heatbed pads, Make a puddle of solder on the heatbed pad, and introduce the tinned end of the wire into this whilst continuing to heat the solder. once the solder flows nicely around the wire. remove the soldering iron, and hold the wire still until the solder sets completely... this will make your task easier
the copper wire will transfer heat so its a good idea to use gloves or pliers to prevent burns.

 the Indicator LED on the heatbed is polarity conscious...  so please be careful to get the wires the right way round. 
Prusa use a twin wire with one black wire, and one red wire,  please match the colours with your new wires. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 07/11/2020 12:35 pm
paulhostettler
(@paulhostettler)
Eminent Member

@joantabb

This is spectacular advise; I have a wee bit of experience soldering repairing a sheared heatbed wire on an Anycubic S, so not 100% noob on soldering.

Is 16AWG the gauge I'll be wanting to order, or was that just the default on your browser?

Thanks again.

 

*as a bit of an update* last night's doorbell wire patchjob is holding! 6h41m later we're 17% into the print! Building a Lovecraft Japanese Castle... time to experiment with 3D Gloop today! Need bigger clamps....

This post was modified 5 months ago by paulhostettler
Posted : 07/11/2020 1:01 pm
paulhostettler
(@paulhostettler)
Eminent Member

Thermal runaway QQ

Guess the patch job is not good enough. Need to order some of that silicone wire cable. Or a new heatbed wire assembly? The one on the Prusa store says it's not compatible with soldered hotbeds? 

Posted : 07/11/2020 2:35 pm
karl-herbert
(@karl-herbert)
Illustrious Member

@cerebratemako

I have installed flexible and heat-resistant silicone cables in all my printers. For this you need the suitable cross sections (AWG14-15 for the 12 or 24V powered lines), crimping pliers and the appropriate plug or screw connections. A simple soldering station and some practice in soldering is also an advantage. Also a simple multimeter.

for example -> MultimeterSoldering station

An investment depends on how much and how often you do such work.

I personally solder a lot and therefore bought equipment from Fluke, Weller and Weidmueller.
This post was modified 5 months ago by karl-herbert
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 07/11/2020 3:06 pm
JoanTabb
(@joantabb)
Moderator

@cerebratemako

16AWG silicone wire,  is conservatively rated at 22 Amps

this is the mk3 forum so the power supply is 250 watts at 24 volts   (Max rated output of the power supply is in the region of 10.5 amps)

the heatbed only uses part of the power supply capability. 

24 volt at 22 amps would be 528 watts,  I think the 16AWG is adequate, 

as you need to solder the wires onto the heatbed, 16AWG will be easier to solder than 14AWG would be. 

the Mk2.5 and earlier printers used 12 volt 250 watt  power supplies. at 22 amps the 16AWG could handle 264 watts... which is more than the power supply can safely handle.

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 07/11/2020 6:22 pm
paulhostettler
(@paulhostettler)
Eminent Member

Okay, so I got some of that silicon 16 gauge wire, swapped out the doorbell wire, lined up another print and....

10 minutes later... Err: MAXTEMP

Boo! I caught it shortly after the error, the extruder, though set to 190, had jumped up past 250.

Previous owner swapped the extruder for a BondTech... perhaps it needs cleaning? Both fans appear to be spinning along merrily.

Posted : 08/11/2020 11:41 pm
JoanTabb
(@joantabb)
Moderator

@cerebratemako

Max temp can be a shortcircuit in the thermistor wiring

regards Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 08/11/2020 11:47 pm
karl-herbert
(@karl-herbert)
Illustrious Member

@cerebratemako

Such extreme temperature jumps usually indicate a defective thermistor or wires. As Joan already mentioned - a short circuit or cable break probably exists. Check the wires while you move them back and forth and also check the internal resistance of the thermistor (about 100kohms at 25 degrees C. room temperature).

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 09/11/2020 9:33 am
paulhostettler
(@paulhostettler)
Eminent Member

So the print nozzle itself was actually, well fused isn't the right word, but it was encrusted with melted filament and adhered into the print. I had to put some effort into breaking it out and peeling the melted filament from around the outside of the nozzle. It's almost as if the nozzle is getting trapped in the print, covered in plastic, and then overheats...

But maybe that's a symptom from a defective thermistor, not the cause.

This post was modified 5 months ago by paulhostettler
Posted : 09/11/2020 1:48 pm
paulhostettler
(@paulhostettler)
Eminent Member

Replaced the extruder thermistor and all was well! Huzzah!

Now there's something crackling with the X-axis belt and print shifting. I made a different thread with picture and video. Thanks for the help!

Posted : 23/11/2020 2:11 pm
karl-herbert
(@karl-herbert)
Illustrious Member

@paulhostettler

What such a small thermistor cannot do! It's good that you were able to solve this problem 😉 and not so good that there is another one waiting for you 😒 .

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 23/11/2020 3:09 pm
paulhostettler
(@paulhostettler)
Eminent Member

@karl-herbert

Well, I did purchase used from a farm, so part of the tradeoff for such a good deal is managing a system with end-of-life-cycle parts issues

Posted : 23/11/2020 4:56 pm
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