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Hello,
I am facing some weird issues and so far I could neither fix them, nor find anything similar on the net... So I thought: lets ask the experts at Dakka, maybe someone had the same issue or any good ideas.

So, printer is an Elegoo Mars 3 pro. Sunlu ABS like Resin.
Great combo for years, 99% successful prints, no hassle whatsoever, great detail.

Now, all of a sudden this happened:
Printy prints the burn-in-layers, then stops lifting the buildplate any higher. It continues printing, but so only always keeps burning in the same areas.
After the print stops, I have to manually raise the buildplate and scrape of all the aprox. 1mm thick puddles that should have been miniatures...

Now, even stranger: the next print might come out perfectly fine, without any issues?! So it cannot be a general issue or defect, like the limiter switch being broken or something like that...?

Things I tried so far:
Recalibrating the buildplate
New FEP film in a new Vat
Cleanup
Checking the screws
Saving the data again to check if it is data-integrity
Lubing the big screw on the buildplate

Things I havent tried so far:
New USB stick...?

Any ideas? I can't make heads or tails of this... Elegoo has great customer service when it comes to spare parts but not in fixing such issues.

Thanks and have a great day,
Garf

I don't have any advice to help you but I am experiencing the exact same issue on my own Mars 3 Pro. The only difference is that mine is fairly new and I've had the issue since I bought it. That may help you rule out mechanical or age-related issues?
I suspect it may be the USB as I've noticed it seems extremely sensitive to me touching it once plugged in.

The buildplate not lifting is a fairly clear indication that something is going wrong on the printer end - this isn't something that should be impacted by your settings/resin etc...

Intermittent errors are a pain to resolve but I'd do the following:

1) Open up the printer and make sure that there are no loose cables from the Zmotor to the motherboard.

2) Reinstall the printer's firmwire

3) Format the USB (FAT32) and use a high quality one (eg Sandisk brand). Worth doing but data corruptoin issues normally manifest more like random sheets of exposed resin through the print or a solid block of resin printing - ergo the zrot keeps lifting things as normal.

4) Take the top off the z-rod and take apart the screw assembly. Check youtube for a guide on this the nut that the buildarm rides on has a spring in it so you have to take it apart carefully. Watch videos to make sure you understand the process. I have heard of these nuts getting chewedup/damaged but that was on some older machines that used plastic nuts. It's worth checking as if it was damaged it could cause random issues

If that fails I'd go to the Elegoo customer support and report the issue and go from there.

You may well have to repeat a load of steps as they go through the problem solving process with you.

Thanks guys, will try different approaches piecemeal.
Tried two prints this morning which both failed (same Chitubox file).
Then tried another, different, much more complicated file - which is printing perfectly right now...
Due to this sometimes working/sometimes not - I don't think it is a mechanical issue.

Will now first try a fresh new USB stick, if that fails then a firmware update.

More suggestions still appreciated!

Update: new USB stick, fresh slices, same issue... So that's not it.
Could it be that Lychee changed something in an update that causes this on some files? One print yesterday was fine without issues, and this only started some 4 weeks ago. Never had this happen before.
Lifting screw works fine, limmiter too.

If it were a lychee issue I'd expect widespread reports considering the Mars 3 is pretty current.

I think you're at the "reach out to manufacturer" stage of things as you've checked over the components; changed the USB; changed the slices; redone the firmwire and all.

It could be something on the motherboard has gone bad.

I have 5x Mars 3 Pro, but that's a new one to me.
Possibly a mainboard issue, or one of the other two boards. If these are damaged, they do weird and inconsistent stuff.
I recently had one where sometimes the printer would turn off when exposure starts on a random layer. Sometimes it didn't happen though.
Elegoo sent me new front and back panel boards, now its working again.

Make pictures and send them to Elegoo with a description, they will try to help you and send you replacement parts when the error has been narrowed down.

Thanks guys!
Update: I cleaned and re-greased the Z-Axis screw at the bacl, as this indeed looked rather worn at the bottom where 95% of the movement happens.
Would make kinda sense, eh? Stuck at the bottom due to the screw not allowing a proper lift.
Alas, next try, same issue again... Plate goes down, prints all layers without going up again... :(
Yeah, probably time for customer service or a new one...

I've had the exactly same issue for months, and honestly, I never solved the problem. I tried same things already mentioned, and different exposure times and lifting distance. It got to the point when I decided to stop resin printing at all. Well, that and the fact that I didnt have enough ventilation in my apartment.

When I've had problems like that on my Halot-Mage, it usually turned out to be an issue with the slicer settings. For whatever reason, Chitubox occasionally likes to set the layer height to 0 except for burn in layers.

Doesn't explain why the file would print right the second time. Maybe the retraction height is being set dynamically in the firmware, the plate gets stuck after burn in and that throws the whole thing off?

Yeah... so my final attempt was: new VAt with new Fep. Recalibrated, Firmware update - same issue.
I have now contacted Elegoo support, as the printer has been bought less then a year ago, I hope they will fix this somehow.

I alsi suspected the slicer, but I've been using Lychee for years with zero problems. And I have been able to brute force print the exact same file. Failed twice, printed fine the third time, so this cannot be it.

Technic is great while it works, but utterly confusing if it doesn't nowadays...

If Elegoo solves the mystery I will update here, in case someone has the same issue in the future.