i3Mk2S - Thermal Runaway...and Smoke  

RE: i3Mk2S - Thermal Runaway...and Smoke

You mentioned in your first post, that servos did a strange sound as well. So the issue might start there. As Joan said, it could by some part on the main board. Try to check the fuse and all power connectors. Disconnect them, check and connect again. If the power connectors are not manipulated for long time, it could get loose. The contact is then poor and it starts to melt down. 

RE: i3Mk2S - Thermal Runaway...and Smoke

@joantabb

Thanks Joan.

Actually, something's wrong there - You said "now the heater doesn't work", but it does. The nozzle gets very hot, but the temperature change doesn't register on the LCD. This is presumably what caused the runaway in the first place.

I've established the thermistor is - probably - OK, so presumably that means the board isn't doing anything to deal with the thermistor signal?

Wouldn't it make sense that there's been a significant failure of the board somewhere, because I'd have thought that the heaters should be fail-safe unless there's a big problem with the board somewhere? I didn't ever expect to see significant amounts of smoke coming from the head.

RE: i3Mk2S - Thermal Runaway...and Smoke

@milos-v

Yes, also, when it failed, it didn't fail and return to the home position. It just stopped with the head down nearly on the bed, at the front left hand side. 

As I said there's a small crater under where the nozzle was (perhaps 1 mm diameter). Can I flat this, or do I need a new bed as well? If so I think it's time to seriously consider whether it's economical to repair it at all.

RE: i3Mk2S - Thermal Runaway...and Smoke

And also just to say, when I switch the machine on, the servos don't move at all. I can't remember whether they home on start-up, or when you start a job...?

RE: i3Mk2S - Thermal Runaway...and Smoke

Just for completeness - I ran a 16 hour job yesterday, overnight with no issues at all. So I can't see it's a firmware issue.

RE: i3Mk2S - Thermal Runaway...and Smoke

You do not need to run a job to test the stepper motor as well as to test the heating. In the Menu - Settings you will find options to move the axes. So you can simply check if it is moving. Also you can set separatelly temperature for hotend and bed as you need.

If the print fails with Thermal runaway message, I think it will not move to end position, it will just stop. In fact this really means a kind of watchdog function. If the heater has a command to heat but the temperature measured by thermistors is not raising or reach the set point, it will raise this message after some timeout to protect printer from causing damage and fire. So the message is not the problem, but a consequence.

Have you checked the fuses and power connectors to on the main board?

RE: i3Mk2S - Thermal Runaway...and Smoke

@milos-v

Ok so I just checked the fuses - all OK.

Checked all the board connectors - all OK.

I then moved the axes manually - all OK.

Then I tried a print from SD:

Everything appeared to work fine - even the nozzle temperature on the LCD increased to the target value. However, once the print started, nothing extruded from the nozzle, and it started smoking again.

I stopped the print and looked once again at the nozzle preheat - the actual temperature on the LCD was back to room temperature, despite the nozzle being extremely hot. There is no way it could possibly have cooled down from the indicated temperature down to room temerature in that time, and as I said, it was still very hot. It was as if the board had got the temperature from the thermistor, and maintained the temperature within limits, but then suddenly lost it when the print started.

One other thing to note was the the bed target temperature for PLA has now changed from 55 deg.C to 60 deg.C. No idea why that's changed.

Thanks.

RE: i3Mk2S - Thermal Runaway...and Smoke

Will start from the end. Target bed temperature is give by the profile. Usually first layer is different then other layers. 

Can you try to move with the thermistor wire while you are measuring the impedance? It could be even the wire is broken, which in fact can be affected by actual position of the extruder. Usually this can happen in the place where the wire joins the other cables, or even very close to extruder, could be mechanical damage. You can switch off the motors and move with the extruder and check, if impedance change.

RE: i3Mk2S - Thermal Runaway...and Smoke

Ok so I poked the meter wires into the plug - open circuit, nothing. When I move the wires around at the head and box connections, there's also no reading - open circuit. I also tried putting the meter probes on the exposed parts of the metal clips on the plug, and again, nothing. Yesterday there was a good reading (as verified by the basic temperature tests). I didn't switch the machine on to jog the motors - didn't seem much point.

I did the same thing with the bed thermistor plug, and the reading was steady at about 120 K Ohms, even when moving the wires around.

So it was either an intermittent fault on the head thermistor, or I've damaged the thermistor sensor by taking it in and out of the head. At this point I've no idea, but the head thermistor now appears to be dead for whatever reason. 

Something tells me that if the thermistor was faulty, whatever triggered the THERMAL RUNAWAY message should have also cut off power to the heater, but it didn't, which to me points to a board issue.

Any thoughts?

Thanks again!

RE: i3Mk2S - Thermal Runaway...and Smoke

Sorry for delay, tomorrow was the last day before closing the restaurants again, so I had a different priority 😉 Are you sure that after thermal runaway error the hotend was still keep heating? It could be just already hot enough to continue burning and smoking....

It still could be broken wire, just day before it was in position to have some contact, now it is in different position. You should try to measure the thermistor directly on the thermistor side if there is some small part without insulation. So you can see if the damage goes to the thermistor or wires.

I do not know how to test the board, had never issue with. I would try to measure maybe voltage on the connectors with try and error. But hopefully somebody could give you a hand with this. What you could do is to test the printer behavior without heating and extruding. You could prepare a gcode which will move the axis, even heat up the bed, but without hotend heating and without extruding. Or unplug the hotend heater cable from the board and run selftest. So everything is tested, just not the heater itself. But test of axes movement is after the heater test, so not sure if this fails, if it continues or stop the test.

RE: i3Mk2S - Thermal Runaway...and Smoke

@milos-v

No problem!

I did try testing at the wires next to the thermstor head yesterday, and it was dead.

I've managed to find a spare thermistor at a local 3D printing shop. It's £5, so for that, I'll try it. I belive there are two versions: 12V and 24V, and I need the 12V version.  I'll just need to replace the plug on the end.

I'll temporarily fit it and see what happens. If it still doesn't work, I'll just buy a new board and genuine Prusa thermistor, and be done with it.

The way I see it, it's either the thermistor or the board? Substituting the thermistor with new will tell me which?

Thanks again.

RE: i3Mk2S - Thermal Runaway...and Smoke

The thermistor does not depend on voltage, but it critically has to be the same impedance charakteristics, otherwise the measurement will be wrong, mean totally wrong.

RE: i3Mk2S - Thermal Runaway...and Smoke

@milos-v

Sorry I was thinking of the heating element, not the thermistor.

Anyway, impedence is the same - and double-checked against the bed thermistor impedence.

It looks identical apart from the connector.

I will solder the new plug on the end, refit, install the latest firmware and give it a go. I will report back in an hour or so!

Cheers!

RE: i3Mk2S - Thermal Runaway...and Smoke

I fitted the new thermistor, updated the firmware and ran the diagnostic checks (x, y, z, hot end and bed) and all came up OK.

I'm currently printing a part form SD; indicated temperatures were fine on startup,  and they increased and maintained as normal.

So far the print looks good.

I think it must have been an intermittent fault with the thermistor, which finally failed as I was checking it the last time.

I just hope the main board hasn't also got an intermittent fault by coincidence!

Thanks to everyone for their help so far. I will update tomorrow when hopefully the print is complete.

Cheers.

RE: i3Mk2S - Thermal Runaway...and Smoke

The first 8 hour print was perfect, and the first of the remaining 3 parts is printing now.

So I'll call it sorted for now.

Thanks all!

RE: i3Mk2S - Thermal Runaway...and Smoke

Good to hear. After any experience like this, next time you will be able to find and solve much faster 😉

RE: i3Mk2S - Thermal Runaway...and Smoke

@dr_gn

I think the thermistors and sensors contribute a lot to malfunctions. For this reason, I would always keep at least 1 of each of these parts in reserve.

good luck and happy printing!

RE: i3Mk2S - Thermal Runaway...and Smoke

Thanks both.

Yes, I think if this kind of thing happens again I'd just substitute the thermistor for a new one - for the sake of £5 it's hardly worth going any further at that stage.

RE: i3Mk2S - Thermal Runaway...and Smoke

My guess is there might be a short or broken wire on the thermistor.  Mind is a MK2 and the E3Dv6 thermistor came with a plug instead of direct soldering to the wire, unlike the later model.  That was the reason why I got the thermal runaway error while I was printing in my earlier days.  After I got rid of the thermistor connector and soldered the wire, the error is gone and everything is working just fine.  You might want to consider remove the thermistor connector and solder directly to the wire.  If yours is soldered, you might want to check for broken wire.  I hope my 2 cents work and happy printing.