As Murphy's Law states "What can happen, will happen". And wouldn't you know, the day after I order a second UM2, my primary UM2 gives me the screen of death, "Temperature error, contact Ultimaker". Well, I'm on a deadline, and my backup printer wont be here for I'm guessing 10 days or so, so I had to do something. So here's what I did.
First, I read the forums. It was suggested to set the advanced mode to "HEAT UP NOZZLE", so I did. Then I started to wiggle the wires until I got the screen of death. Problem was found on the heater block itself.
(I was more focused on fixing the printer than writing a tutorial so you'll have to excuse the lack of good photos)
Next, I disassembled the print-head unit, giving me access to the heater block. From there I removed the heater block using a vise. It was stuck pretty good. Don't forget to remove the set screw that holds the heater filament in... not sure if it holds the temperature probe in...couldn't get a clear visual on weather the hole cut into the probe side or not.
Finally got it out. This image already has the chip removed, but we'll get to that
Next came the indispensable Dremel tool with a very thin cutoff wheel. I very lightly, and very carefully cut into the probe head so I could remove the internals. I did NOT cut all the way through. You can tell when it is far enough because the metal is very thin and takes on a different appearance.
Once the housing was sufficiently split, I carefully pried the shell open far enough that a little light gray plastic looking wad came out. Once I unwrapped the little plastic looking wad, I was ... let's say shocked... that the problem was so tiny. I mean TINY! I immediately cleaned the entire room, vacuumed the floor twice, locked all the doors, and turned the air conditioning off. I simply could not afford to lose this tiny little sensor.
Here it is next to my small razor knife. Yeah...it's tiny.
So, I went about the tedious task of preparing the wires for repair. I pulled the cover off the main board, removed the thermal tab from the board, pulled the wire through the black flex sleeve (knowing that I was going to have to run it back through the sleeve was a downer).
I cleaned the wire up by cutting a little off the end, and stripping the 2 red wires and one clear wire.
At this point I knew the 2 red wires shared a pole on the sensor, and the clear wire had it's own, by looking at how it was wired to the main board. But I had no idea if there was a certain order, so I did a simple "hold them wires on there and see if it'll start" trick. so I temporarily wired up the real "always on" fan so the board would boot, and I don't know if I wasn't holding the wires tight enough to the sensor, but it didn't work the first time (at this point I'm freaking out), Then I switched poles, and SUCCESS! It booted.
I could not, for the life of me, figure out what to use as an insulator material to isolate the red wires from the clear wire and all the wires from the brass hot end. Every thing I looked up had max temp ratings well below 260 C . In the end, I cut a piece of office copy paper about 5mm by 25mm. Basically a little sliver of a piece of paper. I slipped it in between the 2 poles ,or wires, or the 2 silver things that stick out of the sensor...keep up with me here, and and began to wrap the wires. I came up with 25 mm because that's how much paper it took me to create a wrap that was slightly larger than the probe hole on the brass hot end.Then, I carefully twisted it in to the probe hole. Yeah...had to take it back out because I had to feed the wire down the black hollow plastic head unit. Duh...
Short story long (too late) It is possible to do an emergency repair on this sort of thing. Yes, my printer works fine now...yes I have not 1, not 2, but 3 fire extinguishers next to the damn printer now. Yes I learned a lesson, MAKE SURE WHEN YOU DISASSEMBLE YOUR HEAD FOR REGULAR CLEANING THAT THE TEMP AND HEATER WIRES DON'T PROTRUDE FROM THE BACK!!! When the printer homes the head, it will smash those wires against a hot stepper motor...over and over and over again, until the wire fails. I am curious as to how long a quick repair, using office paper and a zip tie to bind the heater wire with the sensor wire, will last. Rest assured I will be contacting Ultimaker for a replacement ASAP.
Hope you enjoyed, I know there's steps missing, and explanations that are vague, but when your printer is down, and you have a deadline to meet, the last thing on your mind will be "Hey lets make a tutorial on jury rigging a temp sensor", unless you're like me (which a lot of you probably are come to think of it)
gr5 edit: reversed the images to what I think they are supposed to be.