Issue with heatbed  

RE: Issue with heatbed

Posted by: @ma-schin

I have my printer now since some months and printed around 5kg of material.

Lastly I had 3 failed prints: Two where the printer stopped and showed an error message about the heatbed failing to reach temperature. The third one had an0hther issue I was not able to identify.

Today I was running several times the self check routine. It failed half of them when the heatbed was tested.

I checked all the cables, nothing obvious wrong there.

Rigth now I am printing and everything is looking find. Expect for the LED on the printbed, it is blinking completely out of any rythm. Not sure if that is new but I think yes.

 

Any ideas what is wrong and what I can do?

 

Thank you! Max

Hello and welcome to the Prusaforum!

I would first check all connections to the heating bed for loose contacts and corrosion. Possibly a line at the heating bed cable is broken and creates a loose contact. The thermistor could also be faulty. If you have a multimeter, measure the internal resistance of the thermistor. It should have about 100 kOhm at 25 degrees C. I would also check the voltage (24V) of the heating bed and the resistance (about 14.4 Ohms).
If this does not help, you might have to do a factory reset and flash the FW again.

RE: Issue with heatbed

I had a print fail last night, roughly 17 hours into a 25 hour print. It had the same error "heatbed failing to reach temperature" on the screen (not the exact text). This was the first time I had ever had this error occur. I ran the self check this morning and the heatbed passed. I've had my Mini about 4 months, printing probably 6-12 hours a day, 5-6 days a week, averaged out. I am running 4.2.1 Firmware. I'm going to try and test the wiring this weekend.

-Audrey

RE: Issue with heatbed

@theaudreye

what temperature were you using for nozzle and bed?

RE: Issue with heatbed

Thank you @karl-herbert for the tips!

I checked all the connections. The screws are thight and the fittins seem ok. There is no corrosion visible. The printer is set up in my living room and therefore in a stable environment.

I checked also the resistance, the reading for the thermistor was 100kOhm and for the heat element around 18Ohm. I was not able to read any voltage but I assume that is my multimeter which may have a broken fuse. The LED on the heatbed is blinking, so there has to be voltage.

Before the first post I already updated the firmware from 4.2.0 to 4.1.1 but I since still have the issue.

Could it be a broken cable which looses contact in certain positions of the y-axis? Can I get a replacement for this cable somewhere?

RE: Issue with heatbed

Posted by: @towlerg

@theaudreye

what temperature were you using for nozzle and bed?

All my prints were 215°C / 60°C.

RE: Issue with heatbed

I use silicone insulated flexible wire for the heatbed cables.    16AWG is ok, 14AWG would be better, 

I have my own crimper to attach the ends.  but If I didn't have a crimper I would consider going to see an auto electrician, or garage engineer... they usually have a selection of crimp terminals and the tool to fit them. 

regards Joan

RE: Issue with heatbed

Posted by: @towlerg

@theaudreye

what temperature were you using for nozzle and bed?

 I was printing PLA nozzle 210 / bed 60

RE: Issue with heatbed

• I did test the resistance for the wires. The thermistor was 103.1 k ohm, which seems to be in range. The bed wire was 5.1 ohm, which is lower than the what is listed by Prusa (6.5-7 ohm). But the heat bed still has passed 3 self bed tests. I don’t know enough about wiring if the 5.1 ohm is bad. 

RE: Issue with heatbed

@theaudreye

Hi, 

A lot depends upon the quality of your multimeter,  at low resistances a tiny inaccuracy can make a large difference

If your printer is passing the tests, it should be ok!

regards Joan

RE: Issue with heatbed

Unfortunately I had another failure with the same exact error. 2 in a row. I contacted Prusa support. After some testing I did they seemed to feel it was the thermistor. So they are sending a new one. fingers crossed it will fix the issue. 

RE: Issue with heatbed

My issue has to be the same one. I printed again and saw the heat bed temperature value jumping from 61 to 57 and back in a second.

I will contact the Prusa support.

Thank you for the help!

RE: Issue with heatbed

Posted by: @ma-schin

I printed again and saw the heat bed temperature value jumping from 61 to 57 and back in a second.

That is what was happening to me. They had me preheat the bed to the ASA setting which is 100ºc. Then I moved the wire harness all over and then the bed (y axis) by hand. I had to use an oven mitt cause the bed was pretty hot to touch. I got the temperature to jump a few times (once it went from 100º, blipped to 30º then back up to 99º) but I couldn't recreate it consistently. The new Thermistor shipped today and I hope to install it this weekend if it arrives in time. I'll let you know how it goes.

-A

RE: Issue with heatbed

@ma-schin

Due to the numerous back and forth movements of the printing bed, the wires can become brittle and fragile over time. Often this cannot be seen with the naked eye and can only be observed with a multimeter while moving the printing bed.
After a broken wire I have replaced all moving cables in my printer with flexible and heat-resistant versions of "Lappkabel", which have so far performed reliably.

https://www.tme.eu/en/katalog/heat-resistant-cables_100565/

RE: Issue with heatbed

The new heat bed thermistor showed up today and I got it installed. I just printed some basic test print stuff and everything is working so far. I’ll try much longer prints this weekend. 

-A

RE: Issue with heatbed

I haven't had any print failures this weekend after printing roughly 30 hours with the Mini. So it seems the heatbed thermistor was the issue. Ma-schin I hope replacing the thermistor takes care of your issues as well.

-A

RE: Issue with heatbed

@ma-schin

were you able to locate the error in the meantime? It would be interesting to know what the cause was - wires or thermistor?