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Two MK4 kits, different results  

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Trilithon
(@trilithon)
Active Member
Two MK4 kits, different results

I have 2 MK4 kit printers. Both assembled by me, passed self tests first try.

Both printed the spatula perfectly in PLA - Same code, same roll of filament. One prints an object in PETG flawlessly, but the 2nd printer, with the same code, same roll of filament strings BAD!

If I drop the temp by 25c, the stringing stops.

Ideas?

Best Answer by Hello:

 

Posted by: @trilithon

A bit more info:

Buddy board: Same revision
Love board: Same revision
FW: 5.0.0
Same gcode file on same USB stick
Same roll of filament

Same environment, printers sit side by side

Really don't want to slice two versions of the same file for different printers, nor do I think I should have to.

Sounds like a faulty thermistor then

Posted : 30/11/2023 12:49 am
Trilithon
(@trilithon)
Active Member
Topic starter answered:
RE:

A bit more info:

Buddy board: Same revision
Love board: Same revision
FW: 5.0.0
Same gcode file on same USB stick
Same roll of filament

Same environment, printers sit side by side

Really don't want to slice two versions of the same file for different printers, nor do I think I should have to.

Posted : 30/11/2023 1:15 am
Hello
(@hello)
Noble Member
RE: Two MK4 kits, different results

 

Posted by: @trilithon

A bit more info:

Buddy board: Same revision
Love board: Same revision
FW: 5.0.0
Same gcode file on same USB stick
Same roll of filament

Same environment, printers sit side by side

Really don't want to slice two versions of the same file for different printers, nor do I think I should have to.

Sounds like a faulty thermistor then

Please help me out by downloading a model it's free and easy but really helps me out https://www.printables.com/@Hello_474427/models

Posted : 30/11/2023 2:40 am
Trilithon
(@trilithon)
Active Member
Topic starter answered:
RE: Two MK4 kits, different results

Hello,

Thanks for the response, that was one of my thoughts.

Seeing what others think before I start throwing parts at it.

Thanks,

Trill

Posted : 30/11/2023 3:12 am
Cary
 Cary
(@cary-2)
Member
RE: Two MK4 kits, different results

I have a MK4 kit and a MK3 ->Mk4.  They were shipped about 5 months apart.  With Input shaping on, one prints matte and the other one glossy.  I reported it and was told that they have a bad bunch of hot end thermistors.  They can't send me a new one because they don't have any "good"  ones to send.  The glossy one with IS is apparently the bad one and the one I prefer.  

Posted : 30/11/2023 4:58 am
Hello
(@hello)
Noble Member
RE: Two MK4 kits, different results

If you contact prusa support they should send you a new one 

Please help me out by downloading a model it's free and easy but really helps me out https://www.printables.com/@Hello_474427/models

Posted : 30/11/2023 6:01 am
Brew
 Brew
(@brew)
Active Member
RE: Two MK4 kits, different results

They do have some in stock. I have one arriving tomorrow that they just sent. Hopefully it's not one of the faulty ones that they're supposed to have. 

Posted : 30/11/2023 4:10 pm
Trilithon
(@trilithon)
Active Member
Topic starter answered:
RE: Two MK4 kits, different results

Chatted with Prusa support, they are sending a new thermistor. 

Posted : 30/11/2023 5:51 pm
Hello
(@hello)
Noble Member
RE: Two MK4 kits, different results

 

Posted by: @trilithon

Chatted with Prusa support, they are sending a new thermistor. 

Thats good

Please help me out by downloading a model it's free and easy but really helps me out https://www.printables.com/@Hello_474427/models

Posted : 30/11/2023 6:06 pm
Trilithon
(@trilithon)
Active Member
Topic starter answered:
RE: Two MK4 kits, different results

I swapped the thermistors between the printers. The printer that was printing perfect started stringing horribly, and the bad printer printed great! So the problem followed the thermistor.

Dunno why I didn't think to swap them earlier, duh.

Thanks for the help and suggestions!

Posted : 01/12/2023 12:51 am
Zappes liked
Brew
 Brew
(@brew)
Active Member
RE: Two MK4 kits, different results

Good to hear. Looking forward to hearing how the new one works. Interesting that the bad one passed the tests. Guess it was only slightly faulty. 

Posted : 01/12/2023 12:58 am
Trilithon
(@trilithon)
Active Member
Topic starter answered:
RE: Two MK4 kits, different results

 

Posted by: @brew

Good to hear. Looking forward to hearing how the new one works. Interesting that the bad one passed the tests. Guess it was only slightly faulty. 

My assumption is that the self test just tests to see if the heater heats up and the thermistor detects it. What value the thermistor sends in this case is erroneous. It is reading 30-40c too low. I have often wondered what the cost would be to add a second thermistor and input on the system to have a double check of sorts to validate the accuracy of the primary thermistor. Another layer of safety too, I mean, what if it have been way off and overheated the hotend?

Posted : 01/12/2023 4:55 pm
Brew
 Brew
(@brew)
Active Member
RE:

 

Posted by: @trilithon
I have often wondered what the cost would be to add a second thermistor and input on the system to have a double check of sorts to validate the accuracy of the primary thermistor.

That reminded me of the quote from the movie Enemy of the State "But who will monitor the monitors"

Having a second thermistor would definitely be a good idea. However, like any other sensor on the printer it would be an added cost that shouldn't be needed unless it was a common issue. Which in my opinion fixing the bad sensor issue in the first place should be the way to go. 

Posted : 01/12/2023 5:20 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: Two MK4 kits, different results

You need to factor in which is correct if you have two, logically you should have three with voting to establish correct reading and a warning for the minority report.

Posted : 01/12/2023 7:07 pm
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