Prints a blob

[jeffgar2000]

My mars has been printing like a dream since before Christmas.


All the sudden it starts printing solid blobs instead of distinct parts.  In other words, I was trying to print 5 parts out of clear and instead of getting 5 parts, I got a blob that was the size of the tank and used up all the resin in the tank.

I am using 42 bottom and 8 layer which is the same setting I had for this resin before.

I tried some white resin that I have had very good luck with and it printed the 5 parts embedded in a 1/16" sheet the size of the tank.

I have cleaned it well many times.

I leveled it before both of those failures.

Any ideas?

Thanks

[cliffyk]

What you describe is not typical of a failed LCD shutter, however if you have indeed been "printing since before Christmas" your LCD is overdue for replacement.

Remove the resin tank and platen, then "print' this file (use Chitubox to "slice" and save it for your resin settings) while observing the LCD.

The file is a simple 120 mm x 68 mm x 2 mm block:



Dry printing it will cause the entire LCD shutter to open--you should see a white block the size of the entire print area (this is my Mars with a new LCD):



But more likely you will see a display marred by dead pixels (individual and clusters, like this but maybe worse):



The LCD shutter wears out because the "crystalline liquid" in the Liquid Crystal Display is negatively affected by the 405 nm near UV light used to initiate curing of the resin. It too is hardened with the hardened cells no longer shifting phase to let light through. Failed individual pixels will often trigger neighboring pixels to fail as well causing clusters of dead cells.

This is not any shortcoming of the LCD used in the Mars, but rather an unavoidable characteristic of current LCD technology. This is why makers of all LCD based SLA printers consider the the LCD to be a consumable component...

[jeffgar2000]

Work has been a zoo this week but I will test this weekend and report back.  I plan to order a replacement screen as well just in case.

[jeffgar2000]

Got a chance to run the LCDTest.stl.  It does have a couple of smallish spots but overall should still work for a while.  I noted where the spots were and I will avoid placing items to print in those areas for a while.  I do have another screen on order and I watched the replacement video.  Looks pretty straight forward.

I think I did figure out the problem though.  There is a very small leak in the bottom of my tank and it has allowed resign to leak onto the screen and cure there.  I always wipe the screen down before prints but I could not feel it through the cloth.  I touched the screen with my finger directly and could tell there was a skim/layer cured on there.  I laid a paper towel that was lightly soaked with IPA and let it sit a few minutes then I picked the cured shape lose with my finger nail and it came right up.

I have new FEP coming and will replace and try again.

I did time the bottom layers and subsequent layers and they are exactly what they are supposed to be.

[cliffyk]

Less obvious than clusters of dead pixels are dead individual cells. The latter cause underexposure of affected areas rather than distinct holes; that could lead to the "blob" you described. in any event, at 8+ months old the LCD needs to be replaced; they go down fast once the damage starts--I have observed profound degradation--from a little bad to compleely "toasted"--over fewer than 12 hours print time after first noticing a problem.