Thursday, 25 January 2018

Prusa MK2s Bed thermal runaway issue

Well It had to happen sometime. My MK2s developed an issue! Hard to believe but true!

I was printing something in ABS (bed at 100C) and suddenly the printer just stopped!

I look at the LCD and it says "Bed thermal runaway"

I did some quick testing and sure enough the bed was reading a lot lower temperature than the infrared thermometer was telling me. (yes these infrared thermometer are notoriously inaccurate, but I know mine is close enough, especially on a black surface like the printed bed)

So I removed the heated bed and this is what I found

Lets take a closer look at that thermistor

It has come free from the tape and it hanging in mid air!
So I pealed back the capton tape, no issues.But the alu tape just tore to bits. So I removed it

I contacted Prusa support, but unfortunately they could not tell me anything about the aluminium tape.
Luckly I had Kapton and Aluminium tape
I added a bunch more tape... to try and stop that happening again.

What I don't know is if the adhesive on my Alu tape will be able to handle the temperature. Ill find out soon...

So what actually happened here? My best guess is that the spiral wrap grabbed the cables and pulled the thermistor out with repeated Y movements. All the cable was pulled threw and sitting the in the electronics enclosure.

I suspect this has happened to others, as looking at the build instructions for the Mk3 they now say the wrap the thermistor cables around the heated bed cable. Which I will now do to my machine.