MBP Keyboard Assembly: Backlight illumination with FTIR
Today I have made an interesting discovery: my 2008 2.4 GHz MacBook Pro is using frustrated total internal reflection (FTIR) for the illumination of its keyboard.
The background to this discovery is that I spilled a bit of salad dressing into my keyboard and since then some of my keys are not working reliable anymore. To be more precise: Some keys I must push two or three times until they produce the letter. Thus, I wanted to look if I could clean the keyboard and what kind of keyboard I would need if I wanted to replace it. I used the MBP iFixit guide to achieve the disassembly (and as I have been a lucky guy also the reassembly).
Anyway, when I removed the keyboard compartment from the MBP’s body I discovered that it consisted of four parts:
MacBook Pro Keyboard Parts
It consists of these four parts:
- The actual keyboard
- Keyboard Scheme Foil
- Dotted Transparent Plastic Sheet
- White Plastic Foil with a small PCB and four white LEDs
The four parts were held together by eight little bent wires.
The white Plastic Foil contains a PCB with four white LEDs that emit light into a transparent plastic sheet through the sides of four holes in that sheet:
MacBook Pro Keyboard Backlight Sheet and Leds
As this sheet is transparent, light that is being emitted into it from the sides will be reflected internally endlessly because of the optical effect of total internal reflection. Anyway, if there is something printed on the transparent sheet this will cause the light to emit in that area:
MacBook Pro Keyboard Backlight Sheet
These spots are lying underneath the actual keys of the keyboard. Thus, only the keys are being evenly illuminated. As the light gets weaker in the outer areas of the transparent plastic sheet more points are printed on the transparent plastic sheet in the outer regions than in the inner regions. This technique is terribly simple, very effective and dirt cheap. Brilliant, Apple!
Why do I care for this? Because FTIR is the technique with which Jeff Han brought up the hype for cheap, large multi-touch surfaces. Jeff Han is better known for his performance at the TED.
Update: When I wrote this blog entry, I was just intrigued by the nice technical solution Apple came up with this backlit keyboard. However, there are some people that can creatively apply my bit of superfluous information: Colorized MacBook Pro Keyboard Backlight by Greg Parker.
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nice knockdown and the links – Jeff Han – were v. interesting but … did you get the keyboard to work again properly as in pre ‘salad dressing’ rather than just reassembled?
and yes it take me awhile to get here …
cheers
reassembling went nice. but… some of the key switches were corroded by the vinegar. nevermind i bought a new internal keyboard via ebay. cost 45$.
cheers
johannes
I was wondering if its possible to buy the keyboard layers anywhere.
hi jake,
no, as far as i know, you cannot.
i looked up for my disassembled pieces but i have not found them yet. i do not know if i threw them away. but they are really simple so maybe you can build them yourselves.
cheers,
johannes
Another question. My whole experiment here is to make my macbook unibody 2.0 non backlit, backlit. I know this is possibe. So i bought a keyboard off ebay but it didnt have the layers. So i need the layers. Another question is, can i take the layers off a macbook pro backlit keyboard. Are the macook pro layers the same? I found one on ebay that is a macbook pro. It has the layers, but it said its non working because there was wine spilled on it. Will that ruin the layers. And how does the cable for the backlit keys work. How does it attach to the keys and board. Sorry if its confusing.
Hope you can help, thanks Jake
hi jake,
there should be (at least) 2 problems connected with your approach:
1: the plug with which your macbook’s keyboard is connected to the macbook’s mainboard is missing the necessary cables for the power of the background illumination led’s.
2: the keyboard sits snugly inside of the macbook. there should not be any space for additional sheets.
however, maybe you can make the necessary changes, anywaz.
Hi Johannes
I’ve got a problem with the backlit keyboard of my MacBook Pro 15″ (european keyboard), pre unibody generation: It is not illuminated equally. The right side is much darker then the rest of the keyboard. I spilled some liquid of over the keyboard. All keys are working perfectly.
Any idea?
Thanks’ for your answer in advance.
Regards, Oliver
hi oliver,
i had the same problems with my mbp keyboard on which i spilt salad dressing.in my case the oil of the dressing was still present on top of the dotted transparent plastic sheet. if there is fluid on this sheet, the refraction index of the sheet will be minimized and most of the light will be emitted in the middle of the keyboard next to the leds and you will get an uneven illumination. but it’s only an optical problem NOT an electrical.
i don’t know if in your case the different sheets stick together in a way that the refraction index of the dotted sheet is minimized or whatever. however, what you could do is to disassemble your keyboard (i.e. disassemble your whole mbp) and clean everything nice and neatly.
cheers
This is essentially the same keyboard as the mid-2009 MacBook Pro has, right? I had a beer spill incident not two weeks after getting my 15″ MBP in June and ever since then the keyboard just has not illuminated like it did pre-spill, particularly at the outer edges.
Regards,
Tom
THANK YOU FOR THIS IV BEEN LOOKING ALL OVER GOOGLE!!! this should be like the first search result. you are awsome!
damn, my son spilt coffee over my keyboard. i’ve got to exchange it again. however, the brown illumination of my keyboard’s backlight looks very … interesting.
@Tom sorry for answering that late: no, i don’t think that this keyboard is the same than the mid 2009 MBPs.
however, the backlight functionality is the same. thus, greg parker’s keyboard (as you can see in the image above) uses a red backlight foil.
Many thanks for this strip down and explanation! I am not particularly technical however yesterday I managed to replace the broken backlit keyboard in my late-’08 Aluminium Macbook with a non-backlit one (the only keyboard I could find after months of looking!), yet retained the backlight functionality by keeping hold of the backlight sheet.
It seems to have worked great (even the keys on the non-backlit keyboard are the same as those on the backlit one so did not need to be replaced!), however the backlight suffers from significant dimming at the edges. Do you think that this is due to the seal of the black plastic sheet being broken (necessary to remove the old keyboard), or is it simply due to a slightly dirty plastic reflector sheet (the one with the white dots)? My reflector sheet wasn’t spotlessly clean when I put it back in as I wasn’t aware of its functionality, and I was wary of separating it from the black sheet separating it from the actual keyboard.
Essentially what i’m trying to get at is whether or not it’s worth going back into the laptop to have a clean – or if the broken seal on the black plastic sheet would render any cleaning useless anyway. I’m hesitant to do this as, as I’ve said, I’m not particularly technical and I’m scared I’ll damage the logic board or any connectors in the process.
Many thanks
Ben
hi ben
judging from what you have written i think that the problem lies within the dirty dotted plastic sheet. in my opinion the black foil does only prevent that light comes out of the keyboard/foil bundle and is being reflected by the aluminum of the keyboard pit of the macbook’s body. this would result in an uneven illumination of the keyboard.
all the magic of the even (and thus also uneven) illumination of the keyboard is caused by the dotted platic sheet. light of the LEDs in the middle of the keyboard bundle is dispersed and reflected endlessly within the transparent plastic sheet (this is what is called FTIR). only if this reflection is disturbed by a different surface (the dots) of the transparent plastic sheet the reflection is disturbed and the light is being refracted. as those dots are under the keys, the keys will be illuminated.
to conclude, i think you could open up your mb again and clean the dotted plastic sheet. it should not come from the black plastic sheet.
cheers
johannes
Hey!
just wandering, if i wash my keyboard*in water) and let it dry for couple of days, will it still work
????
i’m afraid to do that, cause i have no spare keyboard :>
i definitely wouldn’t wash the keyboard because there are metallic parts in there that will corrode if they get wet!!!
Hi John, I have a late 08 MB unibody (uk) with no backlit keyboard so I have fitted 1 myself, wasn’t hard to do. But….OSX still doesn’t give me the option to illuminate the keyboard. F5 and F6 still do nothing. In bootcamp tho running win7, it shows on the screen that the brightness is being adjusted with F5 F6 but the backlight is still out??? eather I have a duff BL or is there something missing in OSX if the MB doesn’t come with a BL as standard?
Hey, I wonder is the progress of replacing keyboard backlight color is same for 09′ MBP with older verison?
what is the best colorizer for red? where to get it? thanks
take a red pen and paint the leds red? i don’t know…
many thanks to you Johannes for your guide ! it was very useful and i’m looking for this(changing backlit color)for so long time !
peace…
shayan