garycmartin

I've managed to get the heated bed working again this afternoon after closer inspection of the cables on the motherboard. The issue appears to be the socket for the heater bed, part of the green screw terminal on the main board. The screw terminal for the brown power lead from the bed shows some signs of excessive heat, it is a little blackened inside and heated enough that the metal inside of the terminal (part that cables the clamp) is jammed due to some plastic deformation inside the terminal (it is 60% closed, turning the screw doesn't open/close it), the end of the brown lead was a little sooty, and darkened. After rechecking continuity on the build plate leads (all were good), I cleaned up the end of the brown lead, applied flux, and some fresh solder to the end and re-inserted it into the 60% clamp gap. It was a tight push fit. I measure 0ohms resistance between the motherboard pcb and the heated bed pcb. Retesting now shows the heated bed is working correctly. My worry is this is only a temporary solution as the screw terminal for the brown socket is not properly clamps the lead. It's also unclear why the brown lead terminal should have gotten hot enough to damage the terminal plastic (maybe the original terminal connection was poor and the higher resistance there caused excess heat or some electrical arcing). Longer term fix options would seem to be: 1) De-soldering the green screw terminal from the mother board and soldering in a fresh replacement. I'm not sure if my soldering iron is a high enough wattage for all that copper, but I could perhaps do this at the local Hacklab where the equipment is a little more heavy duty. 2) Swap out the motherboard pcb with a replacement.

Oh wow, that's great, thanks IRobertI.

My first few prints with PLA-flex (black) were rather a mess, but this was me being overly cautious with the extruder temp and way too fast. The reel has a label that clearly states <= 220C, my prints didn't improve until I had the U2 set to 230C and my print speed down near 10mm/s. Interestingly I had also been running my build plate at 60C as per above comments, but was finding PLA-flex can stick _really_ well and you easily end up ripping your part trying to peel it off the bed. The base of the prints were smooth and glossy, but had a cloudy sheen that was difficult to polish off without causing scuff marks. I'm pretty sure the cloudy sheen is caused by removal and/or shrinkage stress (the base corners were pure black with the cloudy sheen only filling a more rounded centre patch). Anyway I'm having issues with my heated build plate today so the last couple of PLA-flex prints have been on a room temperature bed using the glue stick. Both prints came up great, black and shiny on the base and were much easier to peel off without damage (I had been unable to avoid tearing the previous three prints). Tl;dr PLA-flex (black) printing well at 230C onto room temp (~18C) build plate with glue stick applied.

Thanks gr5! So, yes the nozzle is heating up just fine, I've printed a couple of PLA-Flex prints today at 230C on a cold bed and they came out great. Are you aware of any official/unofficial circuit documentation or labeled photos kicking about? Anybody made a U2 hardware tear down yet and posted to youtube? I'll take another pass at manipulating the wiring along the path and reseating and retesting the cable at both ends (it seemed to work once before, perhaps I'll get lucky). I'll also check the PCB solder joints on the back of the build plate connector (found a forum post about bad solder joints there on some early U2 builds). I'll give support a little more time to respond in case they have something specific to test before I start to digging too much deeper, but I might take a closer look at the board when I'm going back over the cable/connector check and have the base open again. Thanks for the hints.

Yes, had the same thing when my U2 arrived a few weeks back, it was printing fine for a while but it occasionally gave me a bed temp error while printing and I noticed that all 4 wires were very loose (they could just be lifted out, the main cable clip to the build plate was all that was usually keeping them in the socket). FWIW you seem to only get an error reported by the U2 if one of the two thinner temp sensor wires comes loose, if either of the thicker power cables is loose you just get a bed that wont heat up (you can still print in PLA, PLA-Flex by tuning the build plate temp setting to below ambient temp). Unfortunately I had to open a support ticket today with what seems like a different build plate heat issue, here's a description of the issue if any one here has any ideas... About a week ago I had the same issue as I now have again today, the build plate was reporting ambient room temp and not heating up. I checked and reseated all the build plate cables again, all seemed fine. I found the post on the forum that suggests opening up the controller underneath and checking the build plate cables haven't come loose from the main board, they seemed good as well. While I had the printer open and on its side I also checked continuity of the cables between the board and the build plate, they were all working. After sitting the printer back upright, without finding any faults, I booted the U2 back-up and retested a print to discover the build plate was heating up correctly again (intermittent faults are the worse)! The U2 had been working well all week since then, lot's of successful prints, until today. I've repeated all the above without luck. Some extra checks today: - I've tested the resistance of the build plate heat circuit when disconnected, it's 6 ohms (that seems lower than I would expect, but I can't find any documented reference as to what it should be) - When the build plate power cables are disconnected (but sensor wires connected) I've measured the voltage across the build plate power cables when the U2 is set to heat the plate to 50C, it seems to report a correctly looking voltage of ~23V - If the build plate power cables are connected to the build plate, the voltage drops close to 0V, as if it can't power that load - I had another visual inspection of the board underneath the U2 but can not see anything that looks unhappy.

Yes, under that menu you can select an entry and edit the various parameters and save it, it then appears as "Custom 1", "Custom 2", "Custom 3", etc each time you save. Unfortunately you can't seem to edit the names, delete ones you don't want, or re-edit an existing one in place, but pretty sure a factory reset removes them (need to double check, I reset the other day).