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Old 08-30-2018, 01:40 AM   #1
sv2000
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[Hardware Mod] Warm light / redshift on Kobo Glo HD

Hi, this is my first post on this forum, hope you find it useful

I have a Kobo Glo HD, and find it to be a great e-reader, except for some shortcomings. Notably the lack of page turn buttons (something for another day) and the garish white frontlight. While newer e-readers come with adjustable frontlight tone, I didn't solely want to upgrade due to the light. Also many newer readers come with capacitive touch, which I don't like, and lack the removable storage from Glo HD. So I decided to make my Glo HD have a warm frontlight. While on LCD this can be achieved via SW tweaks (reducing the blue channel brightness), since the e-ink display is monochrome, lacking a color filter, we need to modify the HW to change the frontlight color temp.

Note 1: The below procedure involves advanced disassembly of your e-reader and could destroy the frontlight or in the worst case the whole e-reader. I am not responsible for any damages.

Note 2: While the newer models have an adjustable color temperature, since I replaced the white LED with orange, this permanently changes the frontlight color to orange. If you are creative, you could try to replace the white LEDs with RGB, and wire up some control circuit to control the color temperature. However I like to minimize the blue light from screens, so don't mind the orange light all the time. I have also super warm LEDs, almost red, you may want something on the yellow side

Step 1:
Pry open the back of the reader. Remove the four screws holding the mainboard to the display, and the four screws holding the display assembly to the chassis. Disconnect the battery connector and the frontlight and display ZIF

Step 2:
Lift away the mainboard from the display. Gently but firmly push the display from the front, to separate the display assembly from the chassis (be careful not to break the glass in this step.

Step 3:
Peel away the frontlight flex from the display. Desolder the white LED from the flex (SMD rework tweezers are very useful here), and replace with the desired LEDs. I used the LED part number SMS1105OC from digikey and I know it roughly fits, you can use this or any other similar part.

Step 4:
Follow steps 3 to 1 in reverse order to reassemble your reader.

Final thoughts -

The orange LED also has a lower voltage drop than the white. However since the series LED driver (presumably) operates in constant current mode, we can drop in the orange LED without burning them.

As you can also see in the final image, the front is less brighter than the original white light. This is due to the orange LED having a lower brightness rating than the white (almost by a factor of 10, couple of 100 mcd for the orange LED vs 2000+ mcd for typical WLED). However this is okay since I dont use the light at max brightness but at a small fraction.
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Old 08-30-2018, 07:39 PM   #2
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Maybe also of interest: https://www.mobileread.com/forums/sh...d.php?t=286949

Yours seems to be the more direct method. Great if it works for you.

I tried soldering an ebook reader once, let's just say it didn't go too well.
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Old 08-30-2018, 11:11 PM   #3
davidfor
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@sv2000: I can't decide what to say. I'm torn between being amazed and horrified by what you did Both reactions might be based on the fact my soldering skills sound like they are at the same level as @frostschutz's.

But, you do make me think. I have a Glo which the light stopped working a while ago. And another with a broken screen. I'll have to see how hard it is to do a transplant.

All joking aside, it looks like a good job and if it works for you, even better.
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Old 03-27-2019, 03:06 PM   #4
Bulgroz
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Hi, thanks for posting this. I decided not to replace the LED's but to put a slim strip of flash gel in front of them instead. A light orange produced a warmer tone. I can also add that it is not neccesary to remove the print board from the display to do this. The LED strip can be peeled off while still attached at the end. If anyone attempts to do this, note that you only need to cover the LED's with a very thin strip. Do not cover the sticky part of the strip with gel. I did this and the result was visible light leakage at the bottom of the page.
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Old 03-28-2019, 08:31 AM   #5
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Quote:
Originally Posted by davidfor View Post
I'll have to see how hard it is to do a transplant.
eBay has loads of cheap kits with SMD chips. Like FM Radio with a TRF AM.
Practice.
You can also practice with cheap pack of SMD resistors between tracks on strip board.
A 2mm to 3mm flat tip and 30W or more iron is good. Not enough heat on fine tips.
A tiny spot of glue can help.
Also make sure you pre-tin the SMD chips (except ICs) and have NO solder on bit, but it's wiped on a wet sponge.
Trick for SMD ICs: Pre-tin PCB, but no bumps, use fluxed braid if there are shorts or excess. Line up IC and reflow diagonal corners. Then simply press down on all the leads. Doesn't matter if you are soldering 3 or 4 leads at once as long as there was no excess solder.
A pre-heat with a commercial PCB heat gun and fine nozzle helps remove. Never use a Solder Sucker plunger tool except on old vintage tag strips. Use fluxed copper braid to remove solder. SMD/SMT is actually easier to rework than Plated through hole, except for BGA and other parts with connections under the package. They need specialist gear. I simply cut off faulty SMD ICs at the body and then braid to remove debris of leads.

Polarity of the LEDs is important! You can use 3V (2 x AA cells) and a 220 to 1000 Ohm series resistor to check.

Some fine pointed cheap tweezers in bargain cosmetic packs are good for SMD.

I've been doing SMD soldering for over 20 years and I'd not attempt this. Translucent coloured lacquer / nail varnish or a coloured plastic film would be my approach. I'd test with a standalone LED. Bare LEDs ALWAYS need a series resistor.

I got a new kettle and was disappointed that the power switch is illuminated by a too bright so called "White" LED (which must be interesting to power from 230V AC) instead of a neon. A Neon only needs a resistor (about 100K to 220K on 110/120V AC or 220K to 560K on 220/240V AC). They are very long life.
White LEDs don't exist. They are Blue to Violet to near UV with a yellow phosphor. The phosphor wears with age and the light gets bluer/purplely.
RGB LEDs are only use for novelties, indicators or backlights as the spectrum is a narrow red, blue and green spike. Many don't mix the colours well as all are three chips in one package, they also need more than 2 pins unless the red & green are in series and the blue in parallel in reverse, then AC drive can give yellow, blue, simulated white and other shades (but no red, orange, green or cyan)
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Old 03-28-2019, 10:55 AM   #6
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Look like a doable job, what temp did you set your iron ? Did you run into any difficulties with the plastique ?
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Old 11-08-2019, 02:07 PM   #7
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Great job!
Does it really comfortable to read at night after changing the leds?

I am amazed Kobo still updating firmware for these old readers.
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Old 11-08-2019, 02:30 PM   #8
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Just when i upgraded to the libra for the comfortlight you post this?! Lol now i think i might try give my glo hd a new leash in life. Kudos to this and your bravery. Same goes to the comments on applying orange paint.
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