Exposed wire from melted insulation/frayed braid around heating block
Hello all!
I have had the Original Prusa i3 MK3S kit for about 3 years now. Been printing very regularly now. I had a few failed prints and noticed that some hanging wire was knocking my print supports. On closer inspection, I noticed the insulation/braiding around the wire has been melted away (probably from a failed print I left alone and it gunked up the whole heating block).
While the print still prints, I'm worried that eventually this wire will get cut/caught/fail. And if it does, I don't want to risk damaging the rest of the printer.
Can the community help me identify what this wire does, what it will impact should be left alone, and how to best reinsulate/protect the hanging wire?
I've done some searching on the forums and based on this post and the store, it appears to be the 'thermistor' set
https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/wiring-fray-around-hot-end/#post-318622
https://www.prusa3d.com/product/heatbed-thermistor-set-mk3-s/
I'd love some confirmation and if just buying and replacing the whole thermistor is the best step. It seems like there are plenty of Youtube tutorials detailing this.
Also what is the best way to 'tuck' this wire away so it does not impact prints?
Attached pictures for reference.
Thank you in advance,
FigFire
Best Answer by jsw:
It sure looks to me like the frayed wires in the photos above are for the thermistor (heat sensor) and not for the actual heater element.
The thermistor is to the front of the heat block, to the right when viewed from the left side of the extruder, and is in a smaller hole than the heater element. I just double-checked on mine to be sure of the positions, plus I eyeballed a spare hot end that I keep in the crash kit to be absolutely sure.
If this were mine I would most likely first try repairing the insulation by **CAREFULLY** wrapping it with some kind of high-temperature tape, such as 'kapton' tape or a heat-resistant insulating tape from an auto parts store and **CAREFULLY** dressing the repaired thermistor leads above those of the heater, as shown by the green arrows in the photo above.
A more ambitious (and much cleaner) repair would be to insulate the thermistor leads with heat-shrink tubing. This would require either completely removing the thermistor wires from the cable bundle to the extruder, or cutting the wires a few inches away from the thermistor, then carefully removing the remains of the damaged insulation, sliding the tubing over the wires, and carefully shrinking the tubing using a small soldering iron. I would avoid trying to shrink it using a heat gun, as that could easily deform the plastic parts in the area.
As I think about it, you could probably just install heat-shrink tubing in place, dress the wires above the heater wires, and let the tubing get self-shrunk with the ambient heat of the heat block.
You can then solder and insulate (heat shrink tubing) the wires that were cut. I would avoid trying to solder any wires in the immediate area of the heat block. The solder used for electronic work melts at around 200C and temperatures in that range are present around the heat block.
Of course you could replace the entire thermistor assembly. These are available from Prusa or Amazon for less than US $10, but that would require removing and re-threading the thermistor wires all the way to the Einsy.
RE: Exposed wire from melted insulation/frayed braid around heating block
That's the wire to the hotend heater, like this:
https://www.prusa3d.com/product/hotend-heater-cartridge-e3d-24v-40w/
Here it is in the whole assembly
https://www.prusa3d.com/product/assembled-hotend-e3d-mk3s/
There are also two thinner wires for a temperature sensor.
RE: Exposed wire from melted insulation/frayed braid around heating block
That certainly looks like the wires to the heater cartridge. If that’s the case, I would look to either repair/re-align the bare wires (unsure exactly how to do so) or swap out the heater asap.
Here’s the relevant page from the MK3S+ assembly manual:
https://help.prusa3d.com/guide/5-e-axis-assembly_169235
And here’s another angle on the hot end wiring:
RE: Exposed wire from melted insulation/frayed braid around heating block
It sure looks to me like the frayed wires in the photos above are for the thermistor (heat sensor) and not for the actual heater element.
The thermistor is to the front of the heat block, to the right when viewed from the left side of the extruder, and is in a smaller hole than the heater element. I just double-checked on mine to be sure of the positions, plus I eyeballed a spare hot end that I keep in the crash kit to be absolutely sure.
If this were mine I would most likely first try repairing the insulation by **CAREFULLY** wrapping it with some kind of high-temperature tape, such as 'kapton' tape or a heat-resistant insulating tape from an auto parts store and **CAREFULLY** dressing the repaired thermistor leads above those of the heater, as shown by the green arrows in the photo above.
A more ambitious (and much cleaner) repair would be to insulate the thermistor leads with heat-shrink tubing. This would require either completely removing the thermistor wires from the cable bundle to the extruder, or cutting the wires a few inches away from the thermistor, then carefully removing the remains of the damaged insulation, sliding the tubing over the wires, and carefully shrinking the tubing using a small soldering iron. I would avoid trying to shrink it using a heat gun, as that could easily deform the plastic parts in the area.
As I think about it, you could probably just install heat-shrink tubing in place, dress the wires above the heater wires, and let the tubing get self-shrunk with the ambient heat of the heat block.
You can then solder and insulate (heat shrink tubing) the wires that were cut. I would avoid trying to solder any wires in the immediate area of the heat block. The solder used for electronic work melts at around 200C and temperatures in that range are present around the heat block.
Of course you could replace the entire thermistor assembly. These are available from Prusa or Amazon for less than US $10, but that would require removing and re-threading the thermistor wires all the way to the Einsy.
RE: Exposed wire from melted insulation/frayed braid around heating block
On closer examination of the pics, I have to agree with @jsw that these appear to be the thermistor wires, not the heater cartridge wires.
My original thought was that the red insulation for the heater wires had somehow been torn and pulled away from the wires, but that doesn’t seem to be the case.
Regardless, I think a repair will be temporary if you can manage it without breaking a wire or shorting something out. I would personally replace the thermistor and deal with the re-wiring back to the brain box. But that’s just me.
Good luck and don’t forget to pull the power cord before you start on this, whatever you do!
Cheers
RE: Exposed wire from melted insulation/frayed braid around heating block
This is the game plan, thank you so much for the help.
RE: Exposed wire from melted insulation/frayed braid around heating block
Thanks for the explanation and advice. I think I will just buy a thermistor. If I had a shop and some of those materials on standby, I would highly consider it!
Cheers for the help.
RE: Exposed wire from melted insulation/frayed braid around heating block
I keep a 'crash kit' of various items, including, among other things, a complete hot end and printed plastic parts that are most likely to get damaged.
My contingency plan, originally, on plastic parts was if I needed one, book a couple of hours on a machine at our local makerspace, but then Covid hit the fan and the 3d lab there was closed for a number of months, so I printed and kept almost all extruder parts in the event of a Blob Of Doom or meltdown.