Issue with LG IPS237L monitor ... - Page 1
Forum section: electronics / repair

author: saronno
author_rank: Regular Contributor
timestamp: April 15, 2016, 12:25:32 pm
content: Hi, I have a strange issue with a LG monitor.At first, it have persistent images and get "pinkish".I cleaned the lvds cable and situation get better.Anyway, I still have persisten image on the left. Besides,if you watch carefully with a magnifying glass you will seethat the problem is only on "odd" rows ... in other wordsone row is fine but the next one have and issue (less brighteron all the three colors)... and again, good, bad, good, bad ...right side (it's perfect):left side:I am not a tft expert, but my guess is that the line opening the gates havea voltage a bit below standard and so, in the left part on the screen, it doesn'topen completely the transistor (the line has its own impedance so the voltage is not exactly the same along the row). This happen only on "odd" rows .. probably because the voltage on odd and even rows are independent of one another.Am I right?If so, I think I should check VGL, VGH and Vcom ... right?

author: tautech
author_rank: Super Contributor
timestamp: April 15, 2016, 09:07:23 pm
content: MemberRaszshould be able to offer good advice when he sees your thread, maybe you could PM him and provide a link to it.https://www.eevblog.com/forum/profile/?u=12153;area=summary

author: Rasz
author_rank: Super Contributor
timestamp: April 23, 2016, 11:21:52 am
content: bad paneliv seen similar effects where backlight slowly cooks the glass

author: saronno
author_rank: Regular Contributor
timestamp: April 23, 2016, 12:27:09 pm
content: Quote from: Rasz on April 23, 2016, 11:21:52 amEven if the panel has a led backlight?Anyway I send a PM to Dave ... I will try to play with VGL/VGH/Vcom just to see how it will reactand have some fun. I don't have the schematics of course, but I don't think it will be so hard to findthe right feedback resistor to change these voltages playing with a potentiometer.

author: Rasz
author_rank: Super Contributor
timestamp: April 23, 2016, 12:30:05 pm
content: Quote from: saronno on April 23, 2016, 12:27:09 pmespecially, there are lg panels with led string only on right side (afair), and with time that right side goes yellow with weird every second row dimmer effect

author: saronno
author_rank: Regular Contributor
timestamp: April 23, 2016, 12:31:22 pm
content: Quote from: Rasz on April 23, 2016, 12:30:05 pmGood to know ... I will also check where the led stript is located on this model ...

author: saronno
author_rank: Regular Contributor
timestamp: April 23, 2016, 12:33:40 pm
content: However it's not a intuitive idea ... it's strage having this issue on alternate rows, isn't it?Why not all the rows?

author: Rasz
author_rank: Super Contributor
timestamp: April 24, 2016, 04:16:19 am
content: Quote from: saronno on April 23, 2016, 12:33:40 pm

author: saronno
author_rank: Regular Contributor
timestamp: April 24, 2016, 08:40:03 am
content: Thanks, nice video.Anyway, in my case, the issue is on the other side ... so,the cause could be something external (maybe a lamp or somethingheating in the nearby).

author: BMack
author_rank: Regular Contributor
timestamp: April 24, 2016, 09:22:05 am
content: I agree, bad panel. I've seen a lot of bad panels recently, it seems like 75% of the warranty dispatches we get are bad panels.

author: saronno
author_rank: Regular Contributor
timestamp: April 24, 2016, 06:12:54 pm
content: Quote from: BMack on April 24, 2016, 09:22:05 amHow many of them are "real bad panel" ? Since the TCON is integrated with the panel (connected with the tbond) maybesome of them are not real bad panels ... ?

author: Kilrah
author_rank: Unknown
timestamp: April 24, 2016, 06:23:21 pm
content: Well, given it's pretty much impossible to replace the TCON it's considered part of the "panel"...

author: saronno
author_rank: Regular Contributor
timestamp: April 24, 2016, 06:38:57 pm
content: Quote from: Kilrah on April 24, 2016, 06:23:21 pmreplace is impossible but sometimes the tcon is fixable.

author: saronno
author_rank: Regular Contributor
timestamp: October 01, 2016, 04:03:34 pm
content: This afternoon I made some test, just for fun ....I got to integrated TCON ... first thing I saw were a couple of intriguing test points... vgh_o and vgh_e ... these made me think that alternative rowhas different vgh source (o and e I think stay for odd and even).I check them with the multimeter .... they alternate from 30v to -8.5v ,,, fine ...ops ... just a moment, wtf, how could I see this with my multimeter??? Aren'tthey suppose to do that at a certain frequency? So I took the scope ... and this iswhat I got:Second per division was 5.How come is it so slow???

author: saronno
author_rank: Regular Contributor
timestamp: March 12, 2017, 06:29:51 pm
content: is it 4V a bit too low for VCOM?I didn't find AVDD, but VDD is about 10,7V ...VCOM should be about AVDD/2 .... right?