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MK3S resets when bed heater starts  

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Awestruck
(@awestruck)
New Member
MK3S resets when bed heater starts

Hi -

I've recently got an MK3S kit.  Assembled it a few weeks ago and for the most part has been printing great and really reliably.  Much better than another 3D printer I had.  When I got up this morning to start a print, the machine resets when heating the printer bed.  I most recently completed a print late last night, since I had already gone asleep, the printer was on over night.  I tried a couple times to start the print and just as it goes to preheat, the controller resets/power cycles.  I then ran a self test.  Got to heating the print bed and the controller resets/power cycles.

Sounds like perhaps a short circuit which is causing the power supply to cut out briefly.  I'll have to tear things down once I get home from work.  Perhaps starting at the heatbed plastic housing and working towards the controller.  Any recommendation or tips?

Posted : 27/08/2019 10:07 am
timo.m
(@timo-m)
Estimable Member
RE: MK3S resets when bed heater starts

Certainly check for any shorts on the bed heater.

I would also check if the 24V wires from the power supply to the rambo board are screwd down tight. If they are not tight, the 24V Voltage level on the board might drop down when the strong heater on the bed kicks in, resulting in the board switching off due to undervoltage. If you have the necessary equipment you might as well measure the voltage on the bed heating connector when the heating kicks in.

 

Does the bed heat at all or does the printer reset immediately?

Posted : 27/08/2019 11:13 am
vintagepc
(@vintagepc)
RE: MK3S resets when bed heater starts

use a DMM before you move things/disassemble too much to help confirm if there's a short. 

Sounds like you diagnosed it correctly, this symptom is nearly always a short somewhere, and heatbed cables/connections are the first place to start since they move.

There are a diode and LED on the heatbed, if the cables and connections check OK it's not impossible one of those has gone bad. 

Posted : 27/08/2019 11:18 am
timo.m liked
Awestruck
(@awestruck)
New Member
Topic starter answered:
RE: MK3S resets when bed heater starts

Thank you guys.  I'll go through these steps when I get home tonight.

The printer (and heat bed) have been working.  I printed several things yesterday and even the last print of the day was using the heatbed.  So it leads to something worked loose, something has broken, something has rub/worn and perhaps this now shows up when the high current load occurs for heating a room temperature bed.  That is to say, the condition may have shown up earlier in the day but because I was printing back to back the bed was staying warm, no high current, no short.  Of course a dead short should have shown immediately.

I'll report back what I find.

Posted : 27/08/2019 2:34 pm
Awestruck
(@awestruck)
New Member
Topic starter answered:
RE: MK3S resets when bed heater starts

Well...the printer is working again, though a bit unsettling because I don't have a 100% known cause.

I got home, set the printer to unload filament and the heatbed short/reset was still occurring.  (Remember I previously ran calibration/set up routine to see if I could confirm it was heatbed or other heater block).  Just as before, the reset occurred.

I took the build plate off, then did the same preheat test.  Things started heating up just as it should.  Hmm...I changed the build plate and I changed the y axis position.

So, things are working at the moment. I put the build plate back on.  I moved thee y-axis about.  I pushed/pulled/twisted the heatbed cable just a bit to see if I could trigger a reset.  Nothing.  I've not been able to replicate this.  

Thus it must have been something with the way the build plate was set.  I wish I could be more positive.  So I'll just have to put this in the log book for future reference.  

Posted : 28/08/2019 12:42 am
vintagepc
(@vintagepc)
RE: MK3S resets when bed heater starts

I'd still inspect all the heatbed/power connections. They are high current and when things go wrong, they go wrong in unpleasant ways. I'd be VERY wary of something like this not coming back to bite you if you don't know the cause.

Posted : 28/08/2019 1:00 am
timo.m liked
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