Whats wrong with my heated bed (UM2)

[thetastysnail 0]

Hi people.

Ive had my UM2 for about 3 months now. done a lot of ABS prints on it, but around a week ago i had a couple of prints warp badly on it.

then the next print i did i got a temp bed error on the display and the machine locked up.

had to turn it off for a while then it came back on ok.

tried another print and the same thing happened.

so after a week or so of emailing back and forth with ultimaker, (and a few phone calls) they are sending me a new heated bed.

In the process of diagnosing the problems i took a vid of what happens when i try to gradually heat up the bed, manually. thought you might be interested to see it, and maybe some of you experts can give your opinion on what is happening.

for those that don't want to watch the vid, it shows that everything is ok until i set the temp to 60C then the recorded temp shoots up.

 

 

[IRobertI 521]

I'm guessing a bad connection on the sensor. Either a crappy solder joint or the connection to the bed connector. As the bed heats up thermal expansion makes the connection even more glitchy and starts sending weird readings to the firmware that eventually freaks out.

That's just my theory though, no idea if there's any validity to it.

 

[gr5 2,271]

That's my theory also. Reheat the solder joints on that connector. Be warned there may be a "violates warranty" sticker on the connector on some of the newer UM2s. If not go for it. If there is a sticker contact UM Support first.

What country are you in? It makes a huge difference regarding support. Please update your profile settings location to indicate your country *and* then let us know if you have the sticker.

 

[thetastysnail 0]

i read that the solder joints on early printers could be bad, but i dont think mine is an early printer (bought in april). I had a really good look at the solder joints and they seemed ok.

I might take out the heated bed completely and seeing if there is any other place i can identify problems on it.

I am in the UK and i have already ordered a new heated bed. Had to phone them to get it done though cos it was taking ages by email.

 

[thetastysnail 0]

ok i completely removed my heated bed and put it into a room heated to about 60C (actually a paint spray booth on it's bake cycle)

at room temp the temp sensor measures about 108 ohm. at 60C it measures about 190 ohm.

This tallies with what i was experiencing with the bed in operation. ie things go weird at about 60C

I was measuring the resistance directly on the sensor. but i got the same reading if i measured on the connectors also.

Given that i have already ordered a new bed from ultimaker what should i do about this one. I could try getting a new thermistor, and soldering it on.

And should i have had to pay for a new bed given that this one is clearly faulty and the printer is 3 months old.

Rob

 

[thetastysnail 0]

Well in the end it was the thermocouple on the bed that had failed.

I replaced the thermocouple and everything works fine now.

Later today i will upload a couple of pics to show what i did and also what thermocouple i used for the benefit of others who want to do the same fix (it's pretty easy)

everything is working fine now, temps rock steady and confirmed with external temp probe.

I suggest anyone with a bed that won't heat up to try this before getting a new bed (check for loose connections first)

 

[thetastysnail 0]

Seeing as i got a private question asking about this problem, i thought i would complete my description of how i fixed it.

firstly i got one of these temp sensors

http://www.ebay.co.uk/itm/Pt100-222-Thin-Film-RTD-Sensing-Element-Class-A-Platinum-Temperature-Detector-/321161934491?ssPageName=ADME:L:OC:GB:3160

a Pt100-222-Thin-Film-RTD

i think they are easy to find from many places.

i then scratched a small square of coating off the bottom of the heated plate near the connectors.

I glued the sensor on with some thermal epoxy compound. it was stuff i got for glueing heatsinks onto computer components.

I soldered the wires to the connectors (dont think it matters which way round)

i then desoldered and removed the old sensor. making sure there is no solder bridge across the pads.

since then everything has worked perfectly.

see my pics for clarification

 

[gr5 2,271]

I soldered the wires to the connectors (dont think it matters which way round)

 

You are correct: It doesn't matter.

For anyone else who does this, make sure to measure the resistance using an ohm meter at the screws and it should read about 108 ohms. If it reads infinite ohms then check the 2 wires. If it's a short (<10 ohms) then it's probably a problem at the "old" pad where the old resistor was - maybe a solder bridge. 108 ohms is for 20C, you may get 90 or 130 ohms if your room is hotter or colder.