Laptop LED backlight reuse

with 4 comments

My brother had an unfortunate accident with his laptop Acer Aspire V3-771G. He closed laptop hinge but left headphones in between the keyboard and screen. That caused LCD to crack and screen didn’t work any more. Guarantee repair was out of question for its price (170€ / 230$).

REPAIR: I found a replacement screen on German eBay for (87€ shipping included). Having knowledge with disassembling laptop screens, replacing backlights (CCFL on my Lenovo T60) and watching a simple tutorial on youtube I decided I was qualified for it.

broken_lcd screen replaced  88 leds in a row backlight in use

It took me less than an episode of How I met your mother (20 min) to replace it. Brother -> happy.

REUSE; INTRO: I was left with a broken LCD screen but working LED backlight.

I disassembled it in parts and found a ribbon cable from the PCB to LED backlight. It had 1 thick and 8 thin traces. There were 88 LEDs on a small backlight PCB. Which meant there was 1 VCC trace and 8 ground ones for 8 rows of 11 serial LED. White LED work on cca. 3.5V *11= ~40V. I tried powering them directly with 24v (-12V, 12V), most what my ATX computer power supply can provide. It confirmed my expectations. I couldn’t find a datasheet for a LED IC driver number. IC is a boost type converter from 12V to 40ish V. Similar IC. Then a fast search revealed that PCB usually have well designated test points.

CONTROL LOGIC: Points that are crucial are LED_VCCS, GND, LED_EN and LED_PWM. With LED_EN and LED_PWM connected to 5V and LED_VCCS to 12V, backlight turned ON at full brightness.

power and logic wires 88 leds in a row backlight

At VCCS = 12V and 100% PWM LEDs draw 0,6 A current which is 7W power. 12v 1A is needed to power and some kind of simple PWM logic. I made use of STM8S008 I have lying around, with 2 buttons to adjust brightness. I needed 2 input pins and 1 output pwm pin. It was quite a while that if have done a PCB. Laser printer, modified laminator (200°C), 1 part HCL, 1 part H2O2, 2 parts water and voila (if not, repeat the process).

before etching bare board SMD components done

KiCad Schematics and PCB: PCB.7z
Code for STM8S003F3P6: Koda.7z (well commented)
A lot of good materials on this page  (Thank you Mark!)

To protect diffusion layers I bought  thinnest glass available at a near shop (2 mm thin)  cut to size and fit in to replace a broken LCD panel. Had some trouble fitting a metal bezel (lcd was thinner – cca. 1mm)
I plan to add a wooden frame with access to 2 buttons and a power jack.

programming and testing backlight in use

Replaced an LCD assembly, learned to use KiCad, etched a board, soldered it and refreshed programming skills. This thing can be used to redraw something, iterate, see differences or just as a light (a lot of aplications)


Written by luftek

March 1st, 2014 at 2:58 pm

Posted in pcb,Repair,Reuse



4 Responses to “Laptop LED backlight reuse”

This sure looks good. I just came across a broken LED monitor. Wlii surely try. Is there a part 2 ?

luftek says:

Sorry for late replay! :) Part 2? I didn’t make any more of it.

Andrey Garcia says:

i have problem , my monitor cant turn on, i’ve follow the instruction, can you help me?

Troy says:

Thanks for this! Just using the direct power method with 100% brightness. I have no need for PWM as its just gonna be a desk lamp.

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