Bed temperature keeps rising

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janwijbrand
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Bed temperature keeps rising

Post by janwijbrand »

Hi,

Some strange problem occurred. I'm not sure where to look for the cause for it, so hopefully someone over here has an idea..?

After several successful prints with my custom made print bed, now when I want to print, the bed heats up to the desired temperature (40deg in this case), but then it does not stop heating it up. I confirmed this with an infrared temperature reader. Even when the printer's display indicates "0%" power for the bed heat element, the temperature keeps rising up until the point where the fail-safe kicks in and the heater is decoupled (and the print job stops).

I'm guessing the thermistor works, as my infrared reader also tells me the temperature keeps going up. Is there a firmware issue here? What could be the cause of this?

Any suggestion is highly appreciated!
Felix 3.1 single extruder, soon to be Tec 4 dual

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gfeliksdal
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Post by gfeliksdal »

Hi, this seems like a defect mosfet or some kind of short circuit. What were the changes you made for your customer heated bed?

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janwijbrand
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Post by janwijbrand »

Hi, thanks for your reply!

I cut the four wires connecting the heating element to the mainboard, about 20cm from the heating element. The two red wires for the thermistor I soldered back to the thermistor wires of the new heating element. For the white wires I soldered the ends solid and connected them to the wires of the new heating element using a "kroonsteen" (I don't recall the English word for it). In terms of the connecting the new bed, that's what I did. Note that I had about 80 +hours of successful printing time after installing the custom bed.

For some reason I do not think it is a shortcut (but I won't ignore the possibility!). You say it could perhaps be a defect mosfet. Is there any way I can check for that? Where in the board would I find that mosfet? And would replacing the mosfet be in the realm of possibilities?

Thanks again for any input on this issue!!
Felix 3.1 single extruder, soon to be Tec 4 dual

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janwijbrand
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Post by janwijbrand »

Just now I opened up the mainboard housing to check for anything pointing to a short circuit or something amiss with the wiring. Visually everything seems OK.

Doing this however I noticed the red reset button that I **blush** totally forgot about. I never really needed it before. So, I powered up the printer and hit the reset button. Then I set the bed temperature to 40deg. Now, when reaching 40deg it overshot by some degrees, but then the temperature very slowly fell back to about 40deg (slowly fluctuating with plus or minus a several tenths of a degree). Since I didn't trust that one occurrence, I obviously tried a few times more and indeed, the problem seems to be gone for now.

**phewww**

Still, I'm very curious now what the reset button actually reset? What could have been "misaligned" that now is back to normal?

Hoping for more insights from anyone here, but for now I'm happy again :-)

Of course I'll report back when I did more successful print runs and/or something changes.
Felix 3.1 single extruder, soon to be Tec 4 dual

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janwijbrand
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Post by janwijbrand »

The reset didn't help. The temperature control for the heated bed keeps behaving erratically. I opened a support issue about this too. The person who responded couldn't really believe the reset could've helped in this case. And he is right. He was most helpful BTW, thanks for that.

We deduced it indeed probably is a defect mosfet. Probably I broke it when I soldered the heater wires solid as I forgot to detach them from the mainboard first before soldering. Rookie mistake. Stupid.

Replacing the broken mosfet is possible, but somewhat difficult as I understand. I think I will give that a try and if I that doesn't work out, I'll order a new mainboard.

From mistakes you learn :-)
Felix 3.1 single extruder, soon to be Tec 4 dual

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gfeliksdal
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Post by gfeliksdal »

Hello janwijbrand,

Sorry for the late reply. My colleague already helped you, I've heard. Did you manage to replace the mosfet?

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janwijbrand
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Post by janwijbrand »

I didn't yet attempt to replace the mosfet - lack of time really last two weeks. I intend to try it though. I'll let you know how I fare. Thanks for the follow-up!
Felix 3.1 single extruder, soon to be Tec 4 dual

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janwijbrand
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Post by janwijbrand »

I ordered the mosfet and a soldering iron that would be more suited to the task at hand, took care of ESD measures, but all to no avail: I could not even desolder the (presumably) broken mosfet. No matter how much heat I put in, I couldn't get the soldered bond to come loose on the backside of the mosfet. I was warned for this to happen: the ground pad acts as a - apparently- efficient heat sink.

I'll give it one more go once my frustration has subsided and otherwise order a new main board.
Felix 3.1 single extruder, soon to be Tec 4 dual

Dreide
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Post by Dreide »

janwijbrand wrote:No matter how much heat I put in, I couldn't get the soldered bond to come loose on the backside of the mosfet. I was warned for this to happen: the ground pad acts as a - apparently- efficient heat sink.
Another problem might be that the board is soldered with Pb-free solder which requires somewhat higher solder temperatures; moreover, the part might have been glued on, so you might have to use some moderate force to get it off.
First unsolder the single pins while lifting them up with tweezers. You can also cut them off beforehand with a knife - just be careful to not damage the PCB. Especially for unsoldering the big pin, put on a lot of solder first - sounds counter-intuitive, but this helps with the heat conduction from the solder iron to the pin and the Pb-free solder. Good luck!

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janwijbrand
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Post by janwijbrand »

I gave it one more try, but in the end settled for a new mainboard (which turned out to be an Felix 3.0 board, not a 3.1 board. I have no idea what the differences are for the board).

This one now is up and running, and I have running printer again. Thanks for the suggestions and support.
Felix 3.1 single extruder, soon to be Tec 4 dual

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