Heated bed on UM2 no longer reaching temperature

[simon 1]

Hi all, I've been printing fine with my UM2 for many months. My last print came detached and after a little investigative work found the bed temperature was only about 30 degrees C. I haven't changed anything with my setup for about 10 months so it's nothing I've done recently.

The UM2 screen reports back a temperature of 105 (the target temperature), but it reaches this very quickly (about 60 seconds) rather than the expected 10-15 minutes). The actual temperature is about 30 degrees even after 25 minutes.

After about 30 minutes I get:

' ERROR - STOPPED Temp Sensor Bed'

I've swapped over the heated bed for a spare, but this didn't help.

Any ideas?

Thanks

Simon

 

[gr5 2,229]

Please update your settings to indicate that you have a UM2.

Does it report the wrong temp even at room temp? At room temp it should be roughly 20C.

The bed uses a simple resistor to measure current. Turn your UM2 on it's side and remove the 2 screws to remove the larger cover. Remove the larger cover and remove the two wires that go to the temp sensor (temp2). Check the resistance. It should be about 108 ohms at 20C. Anywhere from 90 ohms to 130 ohms is probably normal. While the resistor is connected try jiggling the wires where they go into the heated bed.

You will probably next have to remove the heated bed - it's pretty easy - start with the 3 levelling screws. There's instructions elsewhere. Remove the 2 screws early on that hold the cable to the heated bed down at the back of the heated bed. I think those are the only 5 screws you need to remove (3 leveling, 2 hold down).

Now be careful - there is a sticker about violating warranty somewhere on the heated bed possibly. Make sure that the 4 screws are all tight. Check the resistance at many places. The most common failur point is where the block of 4 screw connectors is soldered to the heated bed. Messing with this solder however may violate your warranty if you are still under warranty and if you have a sticker that says so. Possibly even if you don't have the sticker. I had to resolder those 4 pads and it was very simple and easy and trivial so I don't know why it would violate the warranty.

 

[simon 1]

Thanks GR5. It does read the correct ambient when cold but when heating up it doesn't. The reported temp shoots up but the actual temp is bearly warm. However I get the same result with a different plate, so I'm thinking the error is with the cable or connection at the PCB end or PCB itself.

[gr5 2,229]

Well then heat it up to 40C or whatever and then cut power and measure the resistance at the PCB end (remove the wires first). If the resistance is still correct then yes it's the PCB. For temps below 60C it takes about 1 minute for every 10 degrees to warm up the plate so 3 minutes should get it up to about 120 ohms (50C).

Here is a table showing what resistance corresponds to what temperature:

http://dev.emcelettronica.com/files/u4/Fig0058_0.png

 

[simon 1]

Yep, it was this connection on the heated bed. Unfortunately I couldn't solder mine quite so easily. It failed again after 5 minutes. I can't help feeling that a connector that went through the PCB rather than one than sat on top of it, would be more reliable. This is the 3rd time this has failed for me and don't do that much printing. :-(