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Pekote
(@pekote)
Active Member
Hotend temperature drop down till trigger THERMAL RUNAWAY

Hello,

MK3s Fw 3.9.0-3421

 

Hotend start to heat and then suddenly after 20 min, printing or not... temperature drop till trigger THERMAL RUNAWAY or the printer RESETS ITSELF

 

The problem is more evident when I request to raise the BED temperature.

 

Simple JOB that the printer is not able to perform-> Preheat PLA order (no print, just preheat) -> then Hotend and Bed reach 215/60 -> Order to raise BED to 100°C -> Bed temp raise but Hotend temperature start to drop till trigger Thermal Runaway

 

It seems that the power supply or Einsy board did not manage such amount of power.

 

I have checked all wiring's, in extruder, I checked hotend heater resistor wirings all the way till connector, and it is OK, it measures 15,1 Ohm.

I also checked temperature sensor, and it is about 100KOhm.

Also hotend connector is OK tight and terminals are firmly installed.

Power Supply voltage is 24V at the time of printer RESETS ITSELF, and also I checked 5,1V stable from Einsy board (2 pin connector on the right top).

Ambient temperature is about 22°C

I tried several firmware versions, latest and oldest…. Same problem...

I have some experience, built several prusa printers, I’m pretty confident with cable check and wirings but this problem is killing me.

 

FROM OCTOPRINT->

 

Recv: ok T:172.7 /215.0 B:73.0 /100.0 T0:172.7 /215.0 @:127 [email protected]:127 P:32.3 A:35.8
Send: M105
Recv: ok T:171.2 /215.0 B:73.4 /100.0 T0:171.2 /215.0 @:127 [email protected]:127 P:32.3 A:35.7
Send: M105
Recv: ok T:170.0 /215.0 B:73.6 /100.0 T0:170.0 /215.0 @:127 [email protected]:127 P:32.2 A:35.9
Recv: Error: HOTEND THERMAL RUNAWAY
Changing monitoring state from "Operational" to "Error: HOTEND THERMAL RUNAWAY"
Send: M112
Send: N2 M112*35
Send: N3 M104 T0 S0*34
Send: N4 M140 S0*97
Changing monitoring state from "Error: HOTEND THERMAL RUNAWAY" to "Offline (Error: HOTEND THERMAL RUNAWAY)"
Connection closed, closing down monitor

 

Posted : 25/07/2020 8:28 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

https://forum.prusaprinters.org/wp-content/uploads/2020/07/Video.Guru_20200725_174828894.mp4

 

 

Video showing the problem

Posted : 25/07/2020 9:35 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

https://forum.prusaprinters.org/wp-content/uploads/2020/07/Video.Guru_20200725_174828894-1.mp4

https://forum.prusaprinters.org/wp-content/uploads/2020/07/Video.Guru_20200725_174828894-1.mp4

This post was modified 1 year ago 3 times by Pekote
Posted : 25/07/2020 10:02 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@pekote

I think you have somewhere a loose thermistor contact. Thermal Runaway is a typicly thermistorproblem. Disconnect the plug from the printer board and measure the internal resistance of the thermistor, it should be 100k ohms at 25 degrees c.

Also move the axes during the measurement and check if the resistance changes.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 26/07/2020 12:02 am
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@karl-herbert

Hello Karl, I checked termistor and I'm 100% sure it is OK. I checked cables all the way from extruder to board connectors I have disassembled and assembled the whole extruder for it.

Posted : 26/07/2020 3:40 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@pekote

Thermal Runaway also look here: https://www.help.prusa3d.com/en/article/thermal-runaway-temperature-drops_2131

The wires of the thermistor or heating cartridge can also be brittle within the insulation.
I would possibly still flash the latest firmware. If all of this doesn't work, you better turn to the prusachat.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 26/07/2020 5:01 pm
Michael Goom
(@michael-goom)
Active Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

I have just suffered the same problem this morning. The machine was working all day yesterday still making face shields.

I am getting a Thermal Runaway fault. The hot end heater and thermistor both appear to be working as normal. If I preheat to any of the filament temperatures the nozzle climbs to the set temperature and then appears to stop heating and the thermistor registers the usual decline. I am at a loss as to what to try next. I have re-flashed the firmware, but the results are still the same.

Posted : 27/07/2020 9:45 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@michael-g75

Due to the numerous back and forth movements of the extruder, the leads of the thermistor and/or the heating cartridge may become brittle and temporarily interrupt the contact. This is difficult to detect from the outside. I would always keep a thermistor and a heating cartridge on reserve. These parts can be replaced quickly to check if the fault is in the wires. Most of the time the thermal runaway is caused by defective wires.
 
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 27/07/2020 11:45 am
Michael Goom
(@michael-goom)
Active Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@karl-herbert

Thank you. I will order a new heater and thermistor and give it a try.

 

Posted : 27/07/2020 12:27 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY
Posted by: @karl-herbert

@pekote

Thermal Runaway also look here: https://www.help.prusa3d.com/en/article/thermal-runaway-temperature-drops_2131

The wires of the thermistor or heating cartridge can also be brittle within the insulation.
I would possibly still flash the latest firmware. If all of this doesn't work, you better turn to the prusachat.

I checked all terms of that article. I'm sure the heater is OK, and contacts terminals tighten always good contact.

The printer shows two kind of failures, RESET itself without reason and Thermal Runaway as seen in the video I sent.

This is my 6th Mk3 printer, the latest one I purchased. Running an average less than 5hs / day average.

SN : CZPX2419XK00430503

Posted : 02/08/2020 4:11 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

After a while testing and testing I found the problem. It is the EINSY Rambo 1.1b !!!!

I replaced hotend heater, thermistor for new ones... same failure

I took a second MK3 and used his power supply.... same failure

Finally I moved the EINSY Rambo to another MK3 printer (It was a very big and not easy job) my older MK3 and also started to fail so I conclude that the problem is the EINSY rambo. It is labeled as version "1.1b".

Really sad about it. I have several printers no one of them modified, all original and built by me. 

This is my latest printer bought in June 2019. It has not so much use... not more than 15kg of filament.

 
Posted : 24/08/2020 7:48 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@pekote

That went unfortunatly for you but good that you were able to locate the error. Did you have any other problems with the Einsy before, e.g. melted cable insulation or a short circuit?
The Einsy Rambo is usually quite robust.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 24/08/2020 8:42 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@karl-herbert

Hello Karl, I never have any problem with this one... no short circuit or melted cables, fuses are original. It is quite strange, sometimes it fail soon and sometimes fail after a couple of hours.

To be honest, board change between printers was quite untidy. I moved the suspect Einsy to my oldest MK3, I had to update firm from MK3s to MK3. Fortunatelly failed after 10minutes of print.

Also power supply replacement was a bit untidy, with a couple of cables and screws from old printer to newest printer. 

 

 

Posted : 24/08/2020 9:01 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@pekote

I would turn to Prusa and describe the problem. Maybe you can send them the board for inspection and get a replacement board. It's worth a try as the board is not cheap.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 24/08/2020 9:08 pm
Michael Goom
(@michael-goom)
Active Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

I replaced both the thermistor and the heater cartridge as Karl suggested and still had the same problem. I had re-flashed the firmware to no avail. Having contacted Prusa I did a Factory Reset using the All Data option (7.2.6 in the handbook V3.13) and have had no problems since. I believe that the PID values had become corrupted and they are not reset when the firmware is re-installed. I assume that the values are stored in eprom and would stay with the board when you moved it to a different machine. I am a novice at this so I don't know what really happened, but my printer is now behaving as it always did.

Hope this helps.

Posted : 25/08/2020 8:43 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@michael-g75

I had the same issue a few weeks ago and had to do the same thing.  I am not sure of the cause.  I suspect it happened during an update.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 25/08/2020 9:16 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

@michael-g75

Thanks for the feedback!
I would always do a factory reset when changing boards. Did you change the board now or was the factory reset the remedy?

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 25/08/2020 4:35 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY
Posted by: @michael-g75

I replaced both the thermistor and the heater cartridge as Karl suggested and still had the same problem. I had re-flashed the firmware to no avail. Having contacted Prusa I did a Factory Reset using the All Data option (7.2.6 in the handbook V3.13) and have had no problems since. I believe that the PID values had become corrupted and they are not reset when the firmware is re-installed. I assume that the values are stored in eprom and would stay with the board when you moved it to a different machine. I am a novice at this so I don't know what really happened, but my printer is now behaving as it always did.

Hope this helps.

Thanks Michael, Charles and Karl, I performed all possible factory resets but no luck 😥 . I also tried to reinstall latest firmware and again perform factory reset.

The problem seemed to be some kind of power issue... after a while that bed and heater are turned ON, heater temp drop down. 

I been checking the EINSY board and I noticed that the HEATER/BED LED light turn ON during heating, then blink when reach temperature setpoing as per PWM signal... but after a while BED LED goes to full OFF, no blink,  measuring from control board no voltage/current are present in the connector. So I guess it is related to control board.

I uploaded an image that shows the heater turn ON and OFF and makes some spikes like bad contact or transistor overheat cut off.

I tried to replace fuses.

Really sad about this issue, control boar is expensive.

I had a look in the circuit that is pretty simple, processor pwm out goes to an AND gate with power supply emergency to shut down heater in case of power supply interruption, and then goes to FET transistor.

 

 

 

 

Posted : 25/08/2020 8:11 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

Contact support.  They will be able to walk you through this.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 25/08/2020 8:16 pm
Pekote
(@pekote)
Active Member
Topic starter answered:
RE: Hotend temperature drop down till trigger THERMAL RUNAWAY

I hope I am not a bother with this topic. I found the cause of this problem.

After dig in EINSY schematics, which are quite simple, I found that the hotend heater is being disabled from and AND gate that is used to disable the heaters in case of Power Supply AC  Loss.

I found that the signal "nAC_FAULT" is about 2.5V instead of 5V, so this gives to the AND gate an "uncertain state" ... sometimes HEATER is operative and sometimes not. Due to this 2.5V is not a clear TRUE or FALSE State it is in the middle.

It seems that RV27 Varistor is damaged or R68 is too high therefore Voltage for nAC_FAULT is too low about 2.5Volts.

I had to install a 1.5KOhm resistor from 5V VCC to nAC_FAULT in order to raise voltage of nAC_FAULT to 4V and let the AND Gate to turn on the HEATER.

Resistor is installed in connector J19 between pin3 VCC and pin2 nAC_FAULT.

I know this solution is not optimal but works.

I had to say that this printer was just assembled by me like some others I built in the past. Not so many, I built 6 original prusa printers (Mk2, MK3, and MK3s, plus some MMUs. I have some experience and never had a single electronic fault like this. I don't know were the root cause of this varistor or resistor could rise. 

Find attached a picture with problem description and solution.

Sorry for my bad English.

Posted : 27/08/2020 2:39 am
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