# Casio F91W (mod) Negative Display - DIY



## hansp (Sep 20, 2012)

*DIY Casio negative display mod.*

I just modded my Casio F-91W display.
Thanks to jtstav suggestion.

Here is a simple step-by-step guide to do that:










Original Casio F-91W (before mod).
Remove the screws and back metal case.
Remove the module carefully from the case. (I used small razor-blade)
Peel polarizing film from the screen carefully from the corner using razor-blade, then pull it out slowly using tweezers.
As you can see here, if you rotate the film 90(degree), it'll convert to negative display. However, we can't use that one due to the size.
Cut the linear polarizing film to fit screen dimension. (you have to determine the angle first before cutting the film)
Place it on the display. (it would be easier if you have the film with adhesive on it). Then put the module back, then reassemble the whole stuffs back.
et Voilà! now you have successfully modded your F-91W to negative display.

The trickiest part is when you try to peel off the existing polarizing film and when you try to cut the film the exact same size as the screen dimension.

(ps. this method can be applied to most of Casio / G-shock digital watches)


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## hansp (Sep 20, 2012)

with light in the dark


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## Crater (Sep 11, 2011)

This... looks... epic! :-!

What a great idea, I could never imagine this would work on F91W. Congrats mate, great work.


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## LUW (May 17, 2009)

Pretty cool!


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## kiwidj (Sep 24, 2007)

Looks great! Well done.


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## GS_Leng (May 22, 2012)

Great work there and looking good after the mod!


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## hansp (Sep 20, 2012)

if you see on the picture, there is a white circle element "AH31" behind the back metal plate. What is that? Is that element to produce sound?
I have another watch which sounds too soft, is there a way to replace it?


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## renzo260 (Jun 18, 2012)

nice mod! Mine says hello


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## Crazy Mecha (Sep 13, 2012)

I typically hate negative screens but this turned out great. It almost looks like a whole new watch!


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## vēer (Oct 19, 2012)

Awesome mod, hansp, thanks for putting up this simple how-to, I might try this on my incoming W800H1A !
Im new to this so Id like to ask what kind of  linear polarizing film did you use and where did you buy it?
Im interested in its general characteristics so I can track it down and order it online !

Thanks in advance!


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## hansp (Sep 20, 2012)

vēer;5577609 said:


> Awesome mod, hansp, thanks for putting up this simple how-to, I might try this on my incoming W800H1A !
> Im new to this so Id like to ask what kind of  linear polarizing film did you use and where did you buy it?
> Im interested in its general characteristics so I can track it down and order it online !
> 
> Thanks in advance!


Hi vēer, I bought the polarizing film online at 3dlens.com, I believe they are HongKong-based shop, it took 2+ weeks for me to get the item, but the quality is good.
Good luck! let me know when you have successfully modded your W800


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## DJLin (Jan 4, 2011)

Hi hansp
I really like this mod - excellent work.
Could you tell me which film you bought from the website 3dlens.com?
Or could you PM me the exact model webpage/link?

Thanks!


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## civic98 (May 13, 2008)

I stumbled across this by accident when I was very young, taking apart a calculator, there's an existing film on the LCD that you just need to flip it and the display goes negative, there's no need for a new film. I'm not sure if it's the same with digital watches, or for that matter any digital screens.


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## marcoszam (Jun 14, 2012)

Great job, Mate!

And, a nice pic montage for instruction... Still I feel like the kind of person with the lack of patient and rest of the skills needed to do so, even with this cheap watch.

One more thing is the improvement of the illumination, amazing indeed!










Cheers,
Marcos 

Sent from my HTC One S using Tapatalk


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## dombart (Jan 5, 2014)

Did try it on my trusty W800H beater. The display is almost perfectly square, so in theory you could peel off the original polarizing film, rotate it 90 degrees and stick it on again.

In reality, the film is glued with Glue From Hell (tm) to the display. Be prepared for some tense moments while wriggling it off with a small scalpel blade. Afterwards, the %*&?!!! glue residue will make the film appear opaque and is very diffcult to remove.

So I chose to use a replacement film. Cheapest source for this: Next time you watch a 3D movie, keep the cheapo glasses provided at the theater. The plastic "lenses" are actually the same polarizing stuff. Probably, you will have to flip and rotate the replacement film a little bit about, as the films from the movie glasses seem to be polarized at a 45 degrees angle.

On the W800H, the negative conversion will make the display's separator lines and frames "disappear", as they are not LCD characters but simply printed on the display glass. I like it anyway (ymmv).

Thanks to HansP for the DIY manual!


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## tic-toc/g-shock (Oct 19, 2006)

dombart said:


> In reality, the film is glued with Glue From Hell (tm) to the display. Be prepared for some tense moments while wriggling it off with a small scalpel blade. Afterwards, the %*&?!!! glue residue will make the film appear opaque and is very diffcult to remove.


Thanks for one of the first accurate descriptions of removing the old film. I tried in vain to remove the film on a relatively new GW-M5610 and no way in hell does that old glue come off. With several HOURS of scrubbing with different solvents and oils and blades, there is a tenacity that dares you to remove it completely. I honestly get pissed when I see these mods and noone even mentions it at all but I know my experience was exactly like yours.


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## kung-fusion (Dec 18, 2010)

tic-toc/g-shock said:


> I tried in vain to remove the film on a relatively new GW-M5610 and no way in hell does that old glue come off. With several HOURS of scrubbing with different solvents and oils and blades, there is a tenacity that dares you to remove it completely.


Acetone, about 30 q-tips, and 10-15 minutes is all you need. Yes, it is annoying and some models are worse than others. some fingernail scratching along the way helps


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## dhodesign (Dec 8, 2010)

Thanks for the sharing. Nice info. 

I want to try it with this model. Just need to find polarizing film locally. 

Casio: Classic A-158W Wristwatch photos, videos and specifications A158W | Watch Archive


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## dombart (Jan 5, 2014)

*Finding cheap polarizing film (Was: Re: Casio F91W (mod) Negative Display - DIY)*

As mentioned above, check out a movie theater showing 3D movies. I think the technical term is "Real3D".

If there are only awful movies, just hang around and wait for a show to finish. Usually, there are huge dropoff buckets for used glasses placed near the exit. In most cases, the glasses will become landfill anyway, so you're even helping to preserve the environment ;-).



dhodesign said:


> Thanks for the sharing. Nice info.
> 
> I want to try it with this model. Just need to find polarizing film locally.
> 
> Casio: Classic A-158W Wristwatch photos, videos and specifications A158W | Watch Archive


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## dombart (Jan 5, 2014)

*Using acetone as cleaning fluid (Was: Re: Casio F91W (mod) Negative Display - DIY)*

Yes, acetone will do the trick (if it doesn't, nothing else will). Just be *very* careful not to spill it on other parts of the watch.

It's a rather powerful solvent capable of dissolving/degrading certain kinds of plastic parts of the watch. Also consider wearing surgical gloves for protection, as acetone also can cause skin irritation.



kung-fusion said:


> Acetone, about 30 q-tips, and 10-15 minutes is all you need. Yes, it is annoying and some models are worse than others. some fingernail scratching along the way helps


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## computer_freak (Dec 22, 2013)

*Re: Using acetone as cleaning fluid (Was: Re: Casio F91W (mod) Negative Display - DIY)*

I did something stupid. I tried to move the display up a little, so that I could see where the polarizer was located, but the display popped out completely. I now have trouble fitting the display in between the "sponge" connector and the plastic lip. There is 0 clearance. Is it possible to fix this?


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## Mike K (Dec 5, 2011)

dombart said:


> Did try it on my trusty W800H beater.
> 
> View attachment 1334412


I don't usually like negative displays, and sometimes wish I'd never converted my DW-5600E to negative, but that looks *so* good that I almost want to buy a W800H just to modify it! :-! 



tic-toc/g-shock said:


> Thanks for one of the first accurate descriptions of removing the old film. I tried in vain to remove the film on a relatively new GW-M5610....


Actually, I SUSPECT that there are two accurate descriptions:

1) It seems like most people run into the incredibly tenacious glue that NASA perhaps should have used to attach the heat-resistant tiles to the space shuttles -- has Casio changed their glue formula over the years, or is it perhaps because the watch itself is new?

2) A *few* of us have encountered the "glue? What glue?" situation -- I peeled the film off my 12 year old DW-5600E and saw ZERO residue, making me wonder if I'd managed to peel off the film incorrectly! I don't know if it was the age of the watch (or a lot of UV exposure) that might have made the glue break down, or if I just got lucky, but I cleaned the display with a cotton swab for quite some time before realizing that virtually ALL of the glue had stayed on the old film.


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## dombart (Jan 5, 2014)

*Fixing SNAFUed LCD (Was: Re: Using acetone as cleaning fluid...)*

Ouch. This could be nasty.

Similar problem happened to me some years ago while disassembling the LCD of a Palm Pilot PDA.

In that case, I ended up with taping the display back on with thin transparent tape (as the display was larger than the case cutout, 1-2 mm of display edge were invisible after reassembling the pilot).

The worst problem though was getting the display aligned properly again, as the contacts on the display's edge meeting the one in the frame are %$&?!!! tiny.



computer_freak said:


> I did something stupid. I tried to move the display up a little, so that I could see where the polarizer was located, but the display popped out completely. I now have trouble fitting the display in between the "sponge" connector and the plastic lip. There is 0 clearance. Is it possible to fix this?


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## dombart (Jan 5, 2014)

*White to black and back (Was: Re: Casio F91W (mod) Negative Display - DIY)*

Yup, to be honest, you will use the backlight a lot more often. But sometimes, it's more about the Joy Of Fiddling With Stuff (tm)...

So obviously, I converted this Neolog's (a present from a friend) negative screen to positive. Legibility is really better (if you can call this display legible at all ;-) ...









Hint: It's 9:43



Crazy Mecha said:


> I typically hate negative screens but this turned out great. It almost looks like a whole new watch!


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## timeslowlytickingaway (Jun 5, 2014)

Hi! I just got my Casio F-91W and I REALLY like the mod. I have called around town and no one has adhesive polarized film and the internet is offering me a zillion different types..

Can someone please advise which type of sheet i should buy? Thanks!!


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## Mike K (Dec 5, 2011)

timeslowlytickingaway said:


> Can someone please advise which type of sheet i should buy? Thanks!!


Welcome to WUS! Take a look at this thread as well: https://www.watchuseek.com/f43/how-convert-plain-dw-5600-negative-display-129102.html

I believe it's mentioned in that thread as well, but you can use a lens from the modern "RealD" 3D glasses instead -- the "free" part is great if you're planning on seeing one of those movies anyhow!  If you cut the film from the lens slightly larger than the LCD display, it will stay in place without adhesive.

If you still decide to buy a sheet of polarizing film, you'll probably want the kind that's clear rather than the "frosted" anti-glare film used on LCD TV's and monitors.


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## timeslowlytickingaway (Jun 5, 2014)

Mike K said:


> Welcome to WUS! Take a look at this thread as well: https://www.watchuseek.com/f43/how-convert-plain-dw-5600-negative-display-129102.html
> 
> I believe it's mentioned in that thread as well, but you can use a lens from the modern "RealD" 3D glasses instead -- the "free" part is great if you're planning on seeing one of those movies anyhow!  If you cut the film from the lens slightly larger than the LCD display, it will stay in place without adhesive.
> 
> If you still decide to buy a sheet of polarizing film, you'll probably want the kind that's clear rather than the "frosted" anti-glare film used on LCD TV's and monitors.


Thank you!

He mentions:

I'm going to be taking my plain DW-5600 and 'hopefully' converting the regular display into a negative one with the use of some self-adhesive polarizing film. There have been many questions about where to buy this. I bought mine from Polarization.com (http://www.polarization.com/shop/catalog/index.html) in Texas. The quality was very good, service excellent, and the shipping was pretty fast (3 days). I ordered the thinnest self-adhesive film they had in a relatively small size, part name was: "Linear Polarizer w/adhesive PFA".

but again.. this is the list i am given:

http://www.polarization.com/polarshop/index.php?cPath=21

BUT there is no option for linear polarizer w/ adhesive PFA.. The more i look at my f91.. the more i want it to be modded!!!!


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## acello27 (Sep 4, 2009)

Well done.


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## no-fi (Jul 11, 2013)

Thanks for the instructions and advice.

Has anyone tried this with a Casio F105W? If so, how does the electroluminescence look afterwards?

I want to invert an F105W and put a black Nato strap on - I think the black and blue combo will look sick. I've never modded a watch before but my watch-agnostic girlfriend seems keen to work on a hacking project together, so I'm looking forward to the fun and frustration to come...


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## Geopro (Jan 19, 2008)

Wow! The negative definitely looks better to me.
I own a negative display G (7900) and it looks great but I probably will not purchase another negative.
Too hard for me to see in different conditions (low light). But sure does look great!!!
Yours may be really easy to read - looks like it might be.
At any rate - very cool - and a very nice job!


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## Ronz12 (Oct 8, 2015)

*Re: Using acetone as cleaning fluid (Was: Re: Casio F91W (mod) Negative Display - DIY)*

Hi Guys, need help and infos regarding what film to use. Tried using cheap cellphone polarizing film, they work but the sticky side is on top that you cannot remove the protective film and you cannot stick the other side so it just reversed the display but you cannot simply use it, I have no idea why is it like that and what is the difference with the linear polarizing film that others use ( more expensive thats why I tried the cheap ones from ebay, wrong decision :-( ) any inputs will help, thanks in advance :-!


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## G-fob (Jun 14, 2011)

*Re: Using acetone as cleaning fluid (Was: Re: Casio F91W (mod) Negative Display - DIY)*

3d glasses from movie thearter


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## kosio (Aug 19, 2015)

I used polarising film for an iPhone 4s. Bought it from eBay: http://pages.ebay.com/link/?nav=item.view&id=281815595598&alt=web
It has 2 protective foils on it. One to keep the adhesive side sticky and one to keep the other side... protected


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## JPaolo.Ortega (Dec 19, 2018)

Can i use LCD filters for computer screens?


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## Ottone (Aug 29, 2017)

What kind of glue do you use to put the glass back on it's place in case? Is the watch still water resistant after this mod?


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## kosio (Aug 19, 2015)

Ottone said:


> What kind of glue do you use to put the glass back on it's place in case? Is the watch still water resistant after this mod?


For this mod, there is no need to take the glass out of the case. If the seal is still ok and you put everything back together correctly, it will still be water resistant afterwards.


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## mrcreosoate (1 mo ago)

i remeber doing that in 1977 as a child


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