Repair of dimmed LTN140KT03-403 (samsung monitor for Lenovo T420/T430) - Page 1
Forum section: electronics / repair

author: mlefe
author_rank: Regular Contributor
timestamp: March 15, 2017, 02:19:46 pm
content: Hi all,This is my first post in the forum, although I've been following Dave's videos for more than 6 months nowI've recently obtained some used Lenovo's laptops that have some board issues to and I'm trying to repair them, but this time I'm writing you about the LCD in one of them.This T420 has a LTN140KT03-403 is a Samsung LED display, and I'm trying to find any useful information on it but didn't have any luck (no schematic, general description of how it works, datasheets for the ICs, nothing)The good news is that I have a spare backlight (from a T430) and have narrowed down the issue to the circuit in the LCD, and given that I can see the image (barely) I believe that something must be going on with the IC that handles the PWM.The ICs that I can see on the board are:IC1: HV-EL L23 It's a 16-pin QFN (closest to the connector that goes to the backlight and closest to the big caps and inductors, I suspect handles the backlight)IC2: LA64H-Q LAU5211XOB-E1 (no idea) --> It's a 56-pin QFN (closest to the connector that goes to the laptop: is it the driver for the LCD diodes?)IC5: SiW SW5203 G2316900 1252 --> It's a 48-pin QFN (no idea)I'll be starting my diagnose on the smaller one, the IC1, do you have any ideas/datasheet or schematic that you can share?Big thanks, Martin.-

author: Rasz
author_rank: Super Contributor
timestamp: March 15, 2017, 02:51:22 pm
content: its a $30 used/$50 new part, just swap it?

author: mlefe
author_rank: Regular Contributor
timestamp: March 15, 2017, 03:20:34 pm
content: Hi Rasz,You're right and that's my last option, but to be honest with you, I'm doing more for the sake of learning electronics and the chance to talk about itI believe that the IC5 could be an ADS5203 (10 bit, 40-MSPS ADC) that could make sense... right?Thanks, Martin.-

author: Rasz
author_rank: Super Contributor
timestamp: March 15, 2017, 04:59:25 pm
content: no, those are highly specialized chips designed for one purpose of being on that pcbthey are all made by samsung/lg for internal consumption or _very_ special clients, for example Applehttp://www.ifixit.com/blog/2011/07/19/ipad-2s-new-display-driver-ic/you will not find documentation, unless you are fluent in cantonese (not even mandarin) and have some serious connections in huaqiangbeiwhat you can do is cut a working backlight circuit from cracked LCD controller board with matching led configuration and somehow frankenstein it in place - thats if I understood you correctly that backlight is all thats wrong.

author: mlefe
author_rank: Regular Contributor
timestamp: March 15, 2017, 07:39:34 pm
content: No chance on language or connectionsI think I'm going the frankenstein way... Do you know of a website that can have a diagram of how this LED backlights circuits usually work?That could help me understand where my tinkering should startThanks!

author: Rasz
author_rank: Super Contributor
timestamp: March 16, 2017, 04:10:10 am
content: have you tried basic stuff?there is usually a flex going to the upper edge of the screen - check voltages therelocate and check fuses

author: mlefe
author_rank: Regular Contributor
timestamp: March 16, 2017, 02:10:16 pm
content: Hi Rasz,Yesterday I gave it a go and fixed it! It was a simple thing as you thought: just a fuse and a cap on the monitor's board that were shorting the VLED.I'm happy because it was my first repair of a board with SMD components!Thank you very much for your support, you were part of this!