Weird squiggle on 20x4 LCD

[greencardigan]

Anyone know what would have caused this weird squiggle on my LCD?

It wasn't there a few weeks ago when I last used my roaster controller.

[DavidAlfa]

No idea. Seems like damage to the polaryzer film.
Perhabs some solvent dropped on it?

Maybe made by realtek, slowly showing up,


In any case it needs a new LCD, thankfully inexpensive.
You have some with cool colours here:
https://a.aliexpress.com/_EwZ5zBv

[AVGresponding]

The polariser is made with iodine crystals in a polyvinyl alcohol film. Heat, and damp, can both cause degradation. A slight contamination during the manufacturing process can probably act as a nucleation point.
The film can be replaced, but it's a fiddly job.

[jpanhalt]

Something similar is discussed here: https://www.eevblog.com/forum/beginners/why-i-do-not-like-fractals-on-my-lcd/msg4748645/#msg4748645

It obviously some defect.  Another possibility suggested in that thread is a fungus.

[AVGresponding]

Something similar is discussed here: https://www.eevblog.com/forum/beginners/why-i-do-not-like-fractals-on-my-lcd/msg4748645/#msg4748645

It obviously some defect.  Another possibility suggested in that thread is a fungus.

I'd be surprised if it's a biological vector, iodine is pretty good for sterilising things.

[jpanhalt]

I simply mentioned it as having been discussed here before.  Personally, I would lean more toward a crystallization artifact perhaps from decomposition of the PVA.  As for fungi actually growing in iodine, I agree that iodine is/was widely used as an antiseptic, particularly its complex with PVA.  However, a fungus growing between layers would not be exposed to it. 

Bottom line: There is no definitive answer and those bothered by it, so far as I can tell, have not investigated it further.  Disassembly and microscopic examination to identify which layer is affected would seem to be a first step.  If it is in the polarizer, there are simple things that could be done to help pin its cause down.

[greencardigan]

Something similar is discussed here: https://www.eevblog.com/forum/beginners/why-i-do-not-like-fractals-on-my-lcd/msg4748645/#msg4748645

It obviously some defect.  Another possibility suggested in that thread is a fungus.

Thanks. That does look like the same sort of thing.

I'll have to keep an eye on it and see how quickly it's 'growing'.

[eutectique]

Resembles the tooth marks of a gastropod

[greencardigan]

Just for the record. It's still growing slowly.

[tom66]

I have a TI-84 Plus that has the same kind of defect, but it is black pixels that are 'growing'.

[Psi]

Yep, looks biological to me.

Probably had some bacteria trapped inside during assembly and it just so happened to have enough food and light to grow for a short time.

If you mask it and hit only one side with some bright UV you might be able to prove it's bacteria if only the other side continues to grow.

[H.O]

My fx-9750G has the same sort of thing. Always there no matter if the calculator is on or off.
It came that way when I bought it second hand a while back, I have not (yet) noticed it growing but now I'll keep a close look it just out of curiosity.

[Buriedcode]

I have several displays with these - all of which are old, 20yrs+.  I just assumed it was a delamination of some kind.

[SiliconWizard]

Looks like a pretty standard 20x4 LCD which you shouldn't have any trouble replacing.

[AVGresponding]

Yep, looks biological to me.

Probably had some bacteria trapped inside during assembly and it just so happened to have enough food and light to grow for a short time.

If you mask it and hit only one side with some bright UV you might be able to prove it's bacteria if only the other side continues to grow.

It's not bacteria. Here's a picture of a (simulation of) fractal percolation growth in porous glass and microemulsions:



A brief excerpt:



In any case, many bacteria are resistant or immune to UV: https://www.nature.com/articles/s41598-023-40996-8

[jpanhalt]

In any case, many bacteria are resistant or immune to UV: https://www.nature.com/articles/s41598-023-40996-8[/color][/font][/b]

The paper cited in your link seems to say the opposite.  Your link says:

There is currently no evidence that pathogen resistances or tolerance can be induced following to UV-C irradiation.

Reference 9 is cited for that statement.  It reads:

Choi, H. et al. Can multidrug-resistant organisms become resistant to ultraviolet (UV) light following serial exposures? Characterization of post-UV genomic changes using whole-genome sequencing. Infect. Control Hosp. Epidemiol. 43, 72–78 (2022).

Of course, some microorganisms are more susceptible than others to UV.  Simply shining a UV light on something doesn't mean that something is actually exposed to the UV.  Absorption by intermediate materials (window glass in some cases or cornified epithelium as in the Nature paper) can protect underlying things/tissues from being affected.

[AVGresponding]

In any case, many bacteria are resistant or immune to UV: https://www.nature.com/articles/s41598-023-40996-8[/color][/font][/b]

The paper cited in your link seems to say the opposite.  Your link says:

There is currently no evidence that pathogen resistances or tolerance can be induced following to UV-C irradiation.

Reference 9 is cited for that statement.  It reads:

Choi, H. et al. Can multidrug-resistant organisms become resistant to ultraviolet (UV) light following serial exposures? Characterization of post-UV genomic changes using whole-genome sequencing. Infect. Control Hosp. Epidemiol. 43, 72–78 (2022).

Of course, some microorganisms are more susceptible than others to UV.  Simply shining a UV light on something doesn't mean that something is actually exposed to the UV.  Absorption by intermediate materials (window glass in some cases or cornified epithelium as in the Nature paper) can protect underlying things/tissues from being affected.

You clearly haven't understood what they wrote at all.

"There is currently no evidence that pathogen resistances or tolerance can be induced following to UV-C irradiation" means that non-resistant strains do not become resistant by being exposed to UV-C, in lab conditions. It says nothing whatsoever about extant resistant strains, but implies that UV resistance may be a complex mutation that doesn't happen easily.
This is a good thing in context, as it means UV sterilisation in labs/hospitals etc is unlikely to pose a risk in regards to resistance mutation.

As to the second point, that UV is easily blocked and therefore using it in this case may be ineffective, that only reinforces my point that exposing these displays to UV in an effort to "sterilise" them is unlikely to be useful, even if the problem is a bacterial one and not one of fractal percolation of dielectric relaxation.