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UM3/3x capacitive sensor wire replacement - SOLVED


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Posted (edited) · UM3/3x capacitive sensor wire replacement - SOLVED

As part of the rebuilding of this printer I noticed the wires to the capacitive sensor were frayed.  The white wire in the photo was down to one strand.


Replacing the wire looks to be relatively straightforward, but given the nature of this sensor, I wanted to cross check if there is a specific gauge and type of wire needed for this link.




Edited by JohnInOttawa
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    Posted · UM3/3x capacitive sensor wire replacement - SOLVED

    Hi John,

    I know, your question is different, but there's an official replacement, part # 2014 according to the official parts manual.


    So it could be worth to contact your reseller. The reseller here in Germany lists it as "SPUM-CAAK-SECB"


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    Posted · UM3/3x capacitive sensor wire replacement - SOLVED

    Thank you.  The parts manual is a handy link.  I'll ping my reseller(s) tomorrow.  My guess is I have a suitable wire on hand, I note the twist likely to combat signal issues and wondered if there was anything else special about the setup.


    I'll report back here on what I learn, this little length of wire does seem to be prone to wear out and breakage with age and use.




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    Posted · UM3/3x capacitive sensor wire replacement - SOLVED

    Just an update:  Back in business.  Shout out to Erin at frbc8, and Ken and Felix at Shop3D.ca!


    TD/DR version:  Here is how:


    First, the good news - the official part, 2014 is not expensive.  Depending on the of the print head, I would wager it's a question of when, not if, so I will be planning on having one in my troubleshooting supplies.


    The bad news, right now the part is not in stock locally and transborder mail is deadly slow.

    Still, not all was lost, I was able to narrow down the wire to TR64 UL style 1007, 300V, 90C (more on this in a minute).  7 strand, either 22 or 24 gauge.  I looked around my pile of salvaged parts and found a number of close fits.


    I had never had to work around the capacitive sensor before and did not know which parts were critical.  Erin was able to explain that it measures heat from the bed and give me an idea of what the risks were around the connection.  Protecting the connectors on the capacitve board takes a good magnifying glass and fine tweezers.  Felix was able to fill in the electrical characteristics once we realized there wasn't going to be stock for a while, so I realised I could go a bit long (under a cm) and relieve some strain on the connector ends.


    The next choice was whether to try and re-use any part of the existing cable.  One look at the connector and the crimp-on fittings and I decided the risk of a bad connection and frying a PCB was not worth it.  I found everything I needed on digikey (Canada, but I think this is mutinational).  The cost of everything was swamped by the $8.00 shipping fee so I ordered spares for DIY wastage.


    The two pin female connector is a JST part, available here:



    These are used in all 4 positions at the back of the print head, I picked up a few as I have two UM3s and suspect I am not done fixing them.


    Crimp on sockets for 22-26 gauge:



    Unless you are very good at crimping, I suggest getting a strip of ten.  My first attempt lasted under 15 seconds, the second and third ones went on fine.


    I decided to try two cable assemblies, one pre-assembled with the same female and and the other, the mate.  My hope was that I would save myself the hassle of stripping, tinning etc.  I was partially successful.


    The assembly with the female end, which I hoped to be a direct replacement, was too light gauge on the wire, 26 gauge.  That would be fine for a fan but I elected not to try it on the capacitive sensor.


    The mating male assembly was perfect.



    This assembly is a perfect match for the wire spec at 22 gauge.  I was thrown for a bit when the wire was rated at 80C, not 90C as the original, but then I determined that 1007 wires can be rated at 80C UL and 90C CSA for the same wire.  


    After cutting off the length of black and red cable I needed (being careful to measure the length untwisted), tinning the ends, crimping on the sockets and mounting them into the JST connector, the male connector still had enough wire on it to serve as a continuity tester for my new cable.  I could plug the new female connector into the male and I had 4 wire leads to test the circuit. The same male remnant also fits the fan of course and allowed me to troubleshoot a balky axial fan at the same time.


    It's important to twist the two wires as they were in the original to avoid signal noise.  With that, everything went back together and autolevel and all fans worked first try. 


    Now onto the next challenge, the very slow-heating print bed!




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    • JohnInOttawa changed the title to UM3/3x capacitive sensor wire replacement - SOLVED
    • 6 months later...

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