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UMO - Hot end temperature sensor no longer holds steady. 20 C fluctuations and Max Temp errors.

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The temperature sensor on my UMO seems to have given out. It uses the sensor the the TC2 board.

The sensor will hold for a minute at 180 C (the set point) and will then begin to fluctuate, until the fluctuations get so big that the I get a max temperature error. From what I can tell by looking at the filament, the actual hot end temperature is not running high.

I tried separating the thermocouple wires from the hot end and fan wires, as much as possible. This had no effect.

I tried reseating the connectors and the thermocouple wires. This had no effect.

I inspected the sensor for poor solder joints. It looks fine, though I haven't used an iron to reheat and reseat the joints.

My guess is that the thermocouple wire is broken some place, though I am not sure how that would cause a reading to go high.

What do I need to do to fix this?

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Does it only happen when the head is moving? Or does it happen if you just set it to 180C and sit around and watch?

I guess I would certainly poke all the wires. The thermocouple itself is incredibly simple and it is hard to believe that's the problem if you took it apart and inspected it.

The output of the small board on top of the head is supposed to output 0V for 0C and 5V for 500C and so on in between linearly (there's some magic chip that does this). It seems unlikely the chip is bad but I'd measure the output voltage of that chip while watching the Ulticontroller display at the same time to isolate the fault. Also check that the power going to that little board is steady at 5V.

There's a spare set of wires running from the top of the print head to the PCB underneath. Consider just switching over (both ends of course) to the other cable. It might fix all problems - it did for me. Also there is a green connector where the thermocouple wires go in - those screws somehow got loose on me and I had to retighten those once.

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I think it used to happen only when the head was moving. Now it happens with the head just sitting there. The problem has been slowly getting progressively worse for a while, until today when it seems to have completely failed.

I will have to try your test later. With the thing not working, I decided to take off the hot end and finally give the UBIS a try. The UBIS is working really great. I setup the UBIS to run on the same cables that the stock hotend did, so it seems like they aren't the problem.

As a side bonus, it seems like this was also probably the source of my stringing issues. I am guessing that the hot end was probably running way too hot, due to the malfunctioning sensor. I had previously noticed buldging in the last 30 mm of filament, when I removed it from the hot end (which had also been getting progressively worse), which I am guessing might mean the stock hot end is somewhat wrecked.

Edited by Guest

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gr5 is right; it's probably a loose connection somewhere on the print head. Fluctuations in readings are the first warning, typically. I've had to correct loose connections several time overs the 2-1/2+ years I've had a UMO. I found that the black strain relief clip only increases the frequency of the wires breaking near the clip inside the insulation (where the broken wire is not visible). Having a large free loop in the white connector wires to the tie point well up the Bowden tube reduces the problem to a very low frequency of occurrence. I found a large supply of the crimp-on pins for the white connector housings and they should NOT be soldered to the wires (the factory soldered them on my UMO). The ridged solder creates a stress point right at the pin. Crimp connectors on multi strand wire are the way to go! Most recently, a TC wire loosened right at the green PCB connector.

I've had numerous electrical problems with my UMO (really the only problems after initially sorting our the initial build bugs) and I still have one gremlin that I'll probably never successfully debug. I spent a great deal of time debugging and reworking my Ulticontroller board. It was so unreliable until I manage to correct all the problems from a sloppy assembly, I soldered-in a socket for my LCD display so I could remove the LCD assembly from the base board easily.

Hopefully the new and more expensive electronics in the newer models is of higher quality that what shipped with my UMO.

Edited by Guest

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Hi,

 

I have the same problem.

First I got the max temp error during the print, then it started already before starting the print and the temp on the controller gave 378C.

I have had this before. Then I checked and unplugged and re-plugged the temp wire under the printer and that fixed the problem. But it came back and now I couldn't solve it with that. So I looked at the steel wire next to the temp wire at the hot end. I reordered some loosen wires that touched the block and I increased the distance between the temp and steel wires a little. The print started hopeful, but again I got the max temp error.

@gr5 how can I change to the other wire? I'm afraid I see the other wire, which is meant for another extruder I thought, has 3 wires with different colors as the red and black of the fan.

 

Would be great if you can explain this a little more easy for me...

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You can change to the other cable but I doubt it will help - just change at both ends.  In other words on the head switch to the other wire and then under the printer switch to the other wire there also.

 

First of all set the fan to 70% as this can be partly responsible (not 0% or 100%) .  then set the temp to something, say 60C and wait for the temp to be within 10C of your goal temp because at that point the heater is being turned on and off 20X per second.  Now you have crazy signals going to both fan and heater.

 

Now look at the temp and start poking at the wires and pushing things around.  Push on the head.  While doing this watch the temp to see if it jumps suddenly.  This should give you a hint of where the problem is.  But most likely the problem is at those 2 tiny screws on the print head that hold the thermocouple wires.  Those can get loose.

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I agree. My money's on the screws or the wires/connectors. I have many spare crimp-on connectors and have needed to cut the old ones off and crimp new connectors into place several times in the 5+ years of UMO use. Tiny tools (screwdriver or dental pick) are required to remove the crimp-on connectors from their shell. I use a crimping tool that is very close to the correct model for these connectors. Though it's not the best possible tool for the job, it's much better than needle nose pliers!.

 

The wires often break inside the insulation and make unreliable contact. You can't see the break, because it's inside the insulation. The insulation should be crimped under the 2nd (larger) crimp ring of the connector and the wire NOT soldered. Solder stiffens the multi-strand wire and exacerbates the problem. Through trial and error I've figured out how to support the wires and minimize this problem. I do not route the wires through the black strain relief fingers, because then the wires just eventually break (inside the insulation) at the strain relief fingers. Rather, I go for a long unsupported "bridge" segment from fairly high up the Bowden  tube down to the connector socket on the amplifirer board, with a "U" loop in the wire near the connector. I use a small dab of RTV silicone to tie the wire to the black stress relief fingers, but the RTV is flexible and allows some movement of the wire over a longer length of wire. You need to distribute wire movement and stress over as long a length of wire as possible or you will be plagued by frequent wire failures! Move the wires and move the head around. When I start to see tiny temperature reading fluctuations, I know that a wire/connector repair is in my near-term future, if tightening the wire screws doesn't fix it.

Edited by calinb

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Sorry, but I'm still very uncertain about what to do. I see only one screw holding the steel wire, the temp wire has no screw? Do I understand it right that I have to screw that one screw tight?

I also must say I was printing PETG at 245 degrees.

I made 2 pictures. You see I almost burned the fan wire a year ago, but that was going ok. You can also see that the spare wire of the fan or extra extruder has different colors and has 3 instead of 1 wire. I wonder if just plugging in the black and red plug in the other one is ok.

Sorry, I'm not very technical. Hope you still want to help me.

20171222_115134-2.jpg

20171222_120802.jpg

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Your photos show the heater block.  The problem is very unlikely there.  But at the other end of the temp sensor wires.  On top of the head.

 

There should be a little circuit board there.  That circuit board should have a connector with a wire in it that goes back along the bowden.  That cable is supposed to go through a black plastic E shaped thing that provides strain relief - @calinb was talking about that a lot.  The problem often occurs there.  I was talking about the other connector on the circuit board on the print head - it has 2 little screws that clamp down on two wires that go off to the heater block.  Those 2 screws can get loose.

 

So my guess is those 2 screws.  Calinb's guess is the connector  or the first 3cm of wire nearest the print head as the wire goes along the bowden.

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Thans again for your tips. I have attaché again 2 pictures, this time of the print head.

The first shows the circuit board. I tightened the 2 little screws in the green part with the red and yellow wire. These had loosen a bit, so I hoped this was it. But unfortunately this was not solving the problem. I got the error again.

About the suggestion of the connector, I don't understand which part has tot be replaced. Is it the outer shell at the end, which holdes the colored wires ? Isn't that only a tape to protect? Or do I have tot cut the whole wire and connect with new one? Then I need  to know what kind of wire... I don't know if I am able to do that.

2017-12-22 16.23.08.jpg

2017-12-22 16.34.11.jpg

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5 hours ago, gr5 said:

So my guess is those 2 screws.  Calinb's guess is the connector  or the first 3cm of wire nearest the print head as the wire goes along the bowden.

Actually, I like your guess equally well, Gr5, and I find that my screws need tightening about half the time I encounter these symptoms. The other times, I must switch to my second cable (but I eventually need to repair both cables' open circuits or unreliable wire / connections).

 

Unfortunately, carinac is still having trouble after tightening the screws, but I think I've just about eliminated the problem on my UMO so I'll take some photos today (sadly I'll need to use my smartphone, because my good digital camera is bust). I'll take photos of the metal crimp connectors and my crimp tool too and add a few more tips. There's no good way to correct a broken wire without cutting or pulling the wire apart at the break (slightly shortening the wire, but there's plenty of extra length available "upsteam" by re-doing the spiral wrap) and crimping on a new metal connector. The best way to check for a bad wire is to remove all three metal connectors from the white plastic shell and pull on them with moderate force. If you see the insulation stretch in one area, the wire is broken inside. If the wire breaks completely...well, it was probably broken anyway and you found the broken spot! Check all three wires too; you'll often find that more than one of them is bad.

 

Give me a few hours to shovel some snow here in the wintry inland Pacific NW of the U.S. and I'll get some photos taken and posted for you.

 

 

Edited by calinb

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4 minutes ago, calinb said:

Actually, I like your guess equally well, gr5, and I find that my screws need tightening about half the time I encounter these symptoms. The other times, I must switch to my second cable (but I eventually need to repair both cables' open circuits or unreliable wire / connections).

 

Unfortunately, carinac is still having trouble after tightening the screws, but I think I've just about eliminated the problem on my UMO so I'll take some photos today (sadly I'll need to use my smartphone, because my good digital camera is bust). I'll take photos of the metal crimp connectors and my crimp tool too and add a few more tips. There's no good way to correct a broken wire without cutting or pulling the wire apart at the break (slightly shortening the wire, but there's plenty of extra length available "upsteam" by re-doing the spiral wrap) and crimping on a new metal connector. The best way to check for a bad wire is to remove all three metal connectors from the white plastic shell (it helps to have three hands here) and pull on them one at a time with moderate force. If you see the insulation stretch in one area, the wire is broken inside. If the wire breaks completely...well, it was probably broken anyway and you found the broken spot! Check all three wires too; you'll often find that more than one of them is bad.

 

Give me a few hours to shovel some snow here in the wintry inland Pacific NW of the U.S. and I'll get some photos taken and posted for you.

 

 

 

Edited by calinb

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An update at the last day of 2017 (in the Netherlands is no snow).

I removed the connector and pulled the 3 wires apart from eachother. They didn't break. I replaced the connector and started the print again. It printed well for hours. I think it was a loosen contact.

Thanks all and I wish you a wonderfull  2018! 🎆🍸✨

20171231_195828.jpg

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