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Another power panic / thermal runaway issue  

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BIGUS
(@bigus)
Active Member
Another power panic / thermal runaway issue

I am trying to diagnose what’s wrong with my MK3S.

After successfully printing a ~3.5hr print on Saturday (PETG) attempts at subsequent prints failed. At that point I was running firmware version 3.9.3 which had been working fine, but I began to get power panic errors and thermal runaway issues while printing. The most common error was power panic, or even a simple ‘power loss’ where the screen would dim/blank and the printer would attempt to resume from blackout. My first troubleshooting attempt was to update the firmware to 10.0. This made no difference so I rolled back the firmware to 3.9.3. The issues continued. Through this time I added a UPS as the power source in case there was some fluctuating power (although that hasn’t been a problem). This also didn’t fix the issues. I tried printing after disconnecting the power panic wire and twice experienced thermal runaway. The last print I attempted experienced thermal runaway after the print had started. I believe the current hot end set point at that time was about 250 and I watched as the actual temp dropped at about 1 deg per second until it reached about 25-30 deg below set point and the thermal runaway logic tripped.

I have tested some of the components with the following results (cooled to room temp overnight, unplugged from power)

Heatbed thermistor: 120.9 k ohm

Extruder thermistor: 126.3 k ohm

Heatbed resistance: 2.7 ohm

Extruder: 14.1 ohm

Heatbed voltage: 23.3 V

Extruder voltage: 23.6 V

A self-test run this morning also reports OK for all elements (including hotend and bed).

The heatbed voltage is a hair low and both thermistors seem on the high end (room temp was between 68-72 F) at least according to spec. However I wouldn't expect all this stuff to go bad at once.

Any tips while I wait for customer support to respond?

Posted : 16/08/2021 11:07 am
Diem
 Diem
(@diem)
Noble Member

I would first check that all plugs are firmly inserted, fuses too.  Was there any dimming of other appliances/lights at the same time?  Brownouts and nearby lightening strikes can also cause problems.

Cheerio,

Posted : 16/08/2021 3:51 pm
BIGUS
(@bigus)
Active Member
Topic starter answered:
Another power panic / thermal runaway issue

Thanks Diem,

I hadn't hardly moved the printer, but checked the plugs and thought maybe the power cable into the PSU was loose. Seated that more firmly and still had issues. Nothing else in the house was flickering, and I still had issues after adding the battery backed power supply. I've checked the other plugs and they're still tight.

I was hoping for loose connections until I watched actual extruder temp fall like a rock while still programmed for 250.

Posted : 16/08/2021 5:03 pm
Diem
 Diem
(@diem)
Noble Member

OK, now check the fuses.

Cheerio,

Posted : 16/08/2021 7:12 pm
BIGUS
(@bigus)
Active Member
Topic starter answered:

Checked fuses (all check good continuity and <.3 ohm). After poking/prodding and reattaching plugs I decided to print with a camera on the display to show what's happening. I'm now about 1 hour into the print (including a stop to insert a magnet) and everything's working fine.

Maybe just loose connections although I didn't find any obvious ones.

Posted : 17/08/2021 12:54 am
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