Persistent thermal runaway  

RE: Persistent thermal runaway

You have check both items I have seen.  For me it, it has always been a broken wire.  

RE: Persistent thermal runaway

The hot end stability starts to fail even before the 1st layer completes. You see that in the increased variability before bed temperature makes its rise for 2nd layer. What changes in that time frame?

1. Bad thermistor or its wire/connector (but you replaced it) Overtightened thermistor set screw partially crushing thermistor?

2. Power supply connector loose at EINSY end or power supply terminal blocks

3. Loose wire heater pluggable terminal block.

RE: Persistent thermal runaway

Nothing changes. In other prints, the wobble and fail happens well after the layer change. There might be a correlation between the failure and printing relatively hot. I did a large PLA print after I first changed the hotend bits and that was fine. 

RE: Persistent thermal runaway

You didn't say if you are using an enclosure, or if in AC room air. 

Try adding a good sized fan blowing air into the EINSY case.  If I recall correctly, there were reports with certain firmware builds overheating the heater and/or motor drivers on the board.  

RE: Persistent thermal runaway

It is in an enclosure, and it's generally pretty hot around here.  This would seem to tally with it getting worse when I print hot.

Nice easy thing to test too, cheers!

RE: Persistent thermal runaway

Righty so, I tidied the cables up in the Einsy box, cable tied a 50mm fan to the inside of the box, it moves decent air. Whammo, printing at PETG temp has run for 7 hours. But... the instability has creeped in after a few hours. I bumped the bed temp down 5C and you can see this helps:

Still, there's no way I can print ABS and I used to print that fine. It seems that the load on the bed heater is screwing up hotend regulation. I've seen there's a number of people talking about damaged caps in prox to the bed heater fet. I suspect that's what's going on here. I think the board was damaged from a week long session of printing ABS parts in an enclosure. Sigh.

RE: Persistent thermal runaway

Try at least an 80 mm fan so you can actually move air.  Also - check the reported ambient on the EINSY: if the LCD reads over 40c, you're pushing the limits.

RE: Persistent thermal runaway

That might help, but the board needs fixing anyway. I guess I'll just replace the caps. I need this machine to print ABS so it's always going to be 40C in the enclosure. At least until I actually finish printing the Voron parts and I can relegate this thing to PLA only duties...

RE: Persistent thermal runaway

Replaced the caps, fixed. 

RE: Persistent thermal runaway

Good job on replacing the caps. 

RE: Persistent thermal runaway

Ditto on the fix and especially on getting back here to post your idea worked and was successful. 

Did you by chance read the temp rating on the caps you pulled out? And what temp rating did you replace them with?

RE: Persistent thermal runaway

Also, were you able to get any ESR readings on the bad caps before replacing? Would be nice to have  the ESR values of bad caps for future comparison

RE: Persistent thermal runaway

ESR is rather difficult to test.  I'd be happy to know the brand and part number he pulled ... in lieu of even that, the case rating would be good to know.

RE: Persistent thermal runaway

The caps I pulled were rated at 105C for 1000 hours. This is the part: https://ro.mouser.com/ProductDetail/Nichicon/UWT1V101MCS1GS?qs=sGAEpiMZZMtZ1n0r9vR22cpFQt4dfSbql65FWznHrgYAtnLg%2F2WPFg==

Actually I found it pretty hard even to measure capacitance with them in place. I removed one and it tested at 68uF. I can't test ESR. The other two I had to remove destructively with the twist method because I couldn't really get my iron in there. Their cold state is probably no use anyway. I was able to reliably make the hotend malfunction just by blowing hot air at the board. And in general, the problem had gotten bad enough that the cap would fail after some hours, presumably due to very gradual self-heating (even with a fan, and 40C ambient in the case). 

I fixed the issue by replacing with some really standard caps quite like the ones pictured above, but 35V 100uF. This is fairly convenient to do because you can use their leads to stand off from the board so you can solder them on the pads (bit of heatshrink to cover their legs).

This was just a test to decide if I needed to replace the entire board. I intend to replace all six or so of the on-board aluminium electrolytics with these: https://www.digikey.com.au/product-detail/en/panasonic-electronic-components/EEH-ZK1V101XP/P121401CT-ND/6564659

They are aluminium poly, 125C for 400 hours and *very* low ESR. Not cheap. I think in retrospect, soldering in regular leaded cans will be easier. I'm not sure about fancy aly poly caps with leads of similar specs to the ones I ordered.

From all of this I conclude: It is *critical* to fan cool the Einsy board if you are printing in an enclosure. This failure had me tearing my hair out for weeks trying to figure out what it was. It only took a solid week of printing at 40C ambient to do this damage. Obviously you might get lucky, but I think given the pretty low rating on the existing gaps, you wouldn't want to risk it. I don't know what effect it might have if the caps on the steppers goes bad, it might be subtle...

For the lazy, the easiest way to cool an Einsy is to tidy the cables in the Einsy and cable tie a 50mm fan to the inside of the lid, then cut away the grill over the fan itself. 5V can be found on a connector at the opposite corner of the board from where the fan should be. Obviously you can do better than this, but this is like a ten minute mod that very likely removes the issue from being a problem at all.

As for better enclosure solutions, moving the einsy out of the box is obviously a pain since you'd need to extend a lot of wires. I wondered if you couldn't make a little air vent tube from the side and blow air from outside the enclosure into the back of the einsy. Would probably have to do something about the x motor loom though.

RE: Persistent thermal runaway

Thanks for the detail.  By the way - ESR is hard to measure; low ESR is even harder. Most can't do a decent job of normal ESR (>1 ohm) with average home equipment. ESR in the milliohms requires lab grade equipment (though a quick search found a $100 meter that claims 10 milliohm sensitivity).

RE: Persistent thermal runaway

Posted by: @mat-b

Hi folks. I've a MK3s that reliably errors out with a thermal runaway around half an hour into a print. Let's get all the stuff out the way that isn't the problem. It's not excessive cooling. The hotend is in a sock, and it happens with the fan completely off. It's not the thermistor and it's not the heating cartridge. In trying to fix this I replaced the entire block, heater and thermistor, and they're nicely attached. Seriously, they're fine.

This is what happens when it goes wrong:

This is a large print, it's spent over half an hour on the first layer. You can see there's a point where the temperature is not smooth. Then you see a small drop for the second layer, but the problem continues and eventually the heat crashes and it errors out.

I checked the Einsy thermistor plug, it's solid. The heater plug also, again I changed both of these, and all the wires, re-did the wiring loom in the process. Didn't fix it.

So now the only thing I can think of is some kind of error on the Einsy board itself, either with the MOSFET or the thermistor input. The former is more complex. I don't suppose anyone has heard of a problem with the board like this? Or perhaps has some flash of insight on something I haven't thought of. It's pretty frustrating as it stands. Prusa chat support didn't really go anyway after it became clear it wasn't something obvious.

What is the part number for the caps you replaced?  How many did you replace?  I'm having a similar issue after much troubleshooting.  Thanks!

RE: Persistent thermal runaway

I think you're better off trying to get Prusa to replace your board before you do any repairs, if you can.

The replaced caps didn't actually fix it in the end. I changed a load of stuff including the MOSFET. In the end, I just declared the Einsy a write-off. I tried to action this via Prusa but they asked for close up photos of my soldering work which I just found irritating... So I just bought my own and moved off Prusa stuff for good. Other people might have more patience.

RE: Persistent thermal runaway

Posted by: @mat-b

I think you're better off trying to get Prusa to replace your board before you do any repairs, if you can.

The replaced caps didn't actually fix it in the end. I changed a load of stuff including the MOSFET. In the end, I just declared the Einsy a write-off. I tried to action this via Prusa but they asked for close up photos of my soldering work which I just found irritating... So I just bought my own and moved off Prusa stuff for good. Other people might have more patience.

Thanks for the response.  I ended up just ordering a Fysetc clone einsy.  Got it installed and right when I did the first PID calibration, I got the M112 error.  I've ordered a replacement power supply ( https://www.amazon.com/gp/product/B07VRK86SP/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 ) Going to see if this fixes the issue I'm seeing.  

I've run the silicon sock for a while now but I get this swing where it will be at 245, then 215 at the next polling, then 268, then back to 245.  I've replaced...

Thermistor x 3
Thermal cartridge x 1

Run PID calibration after every part replacement.

Now after this einsy swap, still doing it.

Running the latest firmware.

Running Octoprint but it's all up to date and I've even tried printing from the SD card.

Ran solid for a year with this setup then started to get this M112 error.

Curious now if it's my power supply.  I've had them die in PCs over the years.  Maybe this is the culprit.  It's intermittent.  I can have a print run just fine and then some die.