possibly failing mosfet?

[Farr0wn3d]

Last night I had 2 of the same prints fail, and in the exact same way and more or less in the same amount of time. I came back to the printer on each occasion to find the hot end touching the print and bonded to the surface of the print, and all my temps at room temp with err:MAXTEMP on the LCD.

backstory: these 2 prints are the first prints I've done with Polymaker PC-Plus, as such its the first time I have my MIC6 aluminum plate on the machine instead of the boro and PEI because I didnt want to fuck up my main setup in case I hated the material or the buildtak itself (you supposedly MUST print using buildtak with this stuff). My print temp is set to 270C and my maxtemp in the firmware was set to 285C ( i believe ) but I bumped it up to 300C to hopefully avoid this after the first one.

Heres my theory: if the mosfet is failing, maybe it takes a while for the electronics to get hot in the enclosure (one more thing, I'm running the quiet noctua fan for my electronics case, and it likely moves less air) so eventually, midprint the mosfet faults and lets the temp climb until it hits maxtemp at which time the print halts, but for whatever reason the steppers stay engaged, at least z anyway, because it is giving the hot end enough time to cool down and bond to the print before it times out and drops. starting a print again is no problem.

Thoughts? I have 2 large prints that I need to get done for a customer before monday

[Tim]

Power MOSFETs are pretty robust. If they do fail, it is usually to produce a nearly complete short or open, either of which will kill the heater function. This is much more likely to be a broken thermistor wire, which is just starting to show up with intermittently bad readings. Because of all the mechanical motions, broken wires are always a risk.

Generally, a broken thermistor wire will cause a reading of zero, but because of the feedback, the electronics will try to push the temperture higher, so that when it contacts again, the temperature may be up too high. If you can set a low temperature alarm (don't know if you can), you might catch it reading zero. Or you can just monitor the temperature and see if you can catch it doing something bad.

[Farr0wn3d]

Thats a good point. Is there a log stored for temperature that I can track down? or is there a way of recording a temp log?

Btw yes there is a mintemp shutdown in the firmware as well. Its set to 5C. any time I disconnect my thermistor for swapping out hot ends it throws the error

[jimc]

yeah sound like its time to change out your thermistor or harness going to it. if you turn s3d to the temp graph while it printing you will probably see things arent stable. instead of a nice flat line it will probably be all over the place. if its reading low or bouncing around on the low side then the printer is trying to heat that thing up then all of a sudden it reads correctly and its up over 300 which throws the error.

[innkeeper]

i would preheat thigns, and watch the graph, and move some wires around.
also just monitor it while it is just idle and preheated.

if its a bad wire / connector, you should be able to reproduce it by wiggling wires. if its a bad thermistor, should go wonky while idle and preheated.

i don't wanna scare you, but i had a similar issue, and turned out to be the rambo board itself, so it cost be a bit to fix it.... but from what i have been following on the boards, that is an extremely rare thing.

[Farr0wn3d]

I'm not overly concerned about having to pay money to fix it, I just need it fixed because I'm getting a fair amount of side work for the printer and so its a bad time for it to be unreliable. I may buy a 2nd printer as well.

[Tim]

I just need it fixed because I'm getting a fair amount of side work for the printer and so its a bad time for it to be unreliable.

The main thing is to be pretty sure what the problem is. Because you can go replace the whole RAMBo board, but if the problem is a thermistor wire, then that's not going to solve it. As has been suggested, just bring up the temperature monitor in Simplify3D or pronterface, whichever one you have/use, and check for flakiness in the temperature readings, and make sure you wiggle the wires.

If you come to the conclusion that it really is the RAMBo at fault, and if you have a single extruder, you can change the extruder heater and thermistor connectors from the first extruder to the second, and then reassign (the pins for) those connectors back to the first extruder in the firmware. It's a bit involved, but if you've ever flashed the firmware before, you might find that simpler than buying and installing a new controller board. However, I would put the chance of it being a flaky thermistor wire at something like 90%.

[Farr0wn3d]

I switched to one of my other v6's and the problem didnt persist. or so it seems. the print still failed but this time it was for lack of bed adhesion. I've attempted this print 6 times now, 4 with polymaker pc-plus and 2 with taulman tech g. tech g warped both times. and pc plus warped one time maxtemp error 2 times and I'm on the 4th attempt. I may run out of material before I run out of stubborn-ness..

On another note, I'm considering getting a 2nd printer so that when I have larger jobs I can break it up between 2 printers. Does anyone have any experience with ultimaker 2+? theres one for sale in my city and its a good price. got me thinking..

[jsc]

Not really the place to plug or trash non-MG printers.

[innkeeper]

I've been looking into some large format 3d printers recently... but noting really floats my boat at a cost i am willing to pay.
i've been toying with the idea of building my own.

lots of stuff out there though... a few here run multiple m2's and are very happy.

best place to learn about a printer is go to thier support forums and read a bit... usualy you get a really quick idea on how they perform.

i've found that most industry reviews border on popaganda, so take them with more then a grain of salt.

but i have to believe you can come to the core of your fault pretty quick... give the folks at MG a call or drop them an email if you havent already.