electronics, repairs, service manuals and datasheets discussion community for the repairs professionals and technicians
FAQSearchMembersGroupsRegisterProfilePM'sLogin/Out
LG LCD 575MS problem with brightness

 
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Equipment Repairs
View previous topic :: View next topic  
Author Message
Pep Boix
Guest





PostPosted: Tue Dec 13, 2005 4:40 pm    Post subject: LG LCD 575MS problem with brightness Reply with quote

Hi all

First of all , txs for helping me
I've an old TFT monitor that is experiencing a problem.
The problem is simple .... It works well ... then suddenly it comes ultrabright ... quite white. The picture is quite impossible to view due to the extreme brightness ...
It can be more than 1 hour like this and suddenly again return to the correct brightness. Each time the balance time well/bad is lower (more time bad than well).
The model is LG FLATRON LCD575MS and I have the schematics downloaded from this page but i don't know wich is the problem.
Another thing to be considered: The behaviour is the same without PC signal .... The OSD menu is bright too

Txs in advance

Pep
Back to top
Pep Boix
Guest





PostPosted: Tue Dec 13, 2005 10:16 pm    Post subject: Seems is finally down Reply with quote

Hi again

Seems is always with brightness ...
Well I think it's whiter than brigther ... it's very complicate to say for me

Txs again,
Back to top
Philip
Guest





PostPosted: Wed Dec 14, 2005 9:04 am    Post subject: LG Flatron Reply with quote

Suggest you check the supply to backlight cct ie transformer ( I dont hv the cct, but I think it is 12VDC) Also check the value of the backlight transformer capacitor value ( tuned cct). Good luck.
Back to top
Pep Boix
Guest





PostPosted: Wed Dec 14, 2005 3:45 pm    Post subject: LG Backlight Panel Reply with quote

Hi all again

Txs for your advice Philip. I'll try!!!
I'm working in a company with electronics lab, so if anyone can tell me where is the backlight PCB maybe i can convince the lab workers to test some components to see if it's all ok or it's something about the mentioned capacitor or the transformer.
If the problem is the capacitor i think it'll be easy to fix.

See you and txs again

PS: I have the schema downloaded from this site (LB575EE) but i don't know where the capacitor is
Back to top
Pep Boix
Guest





PostPosted: Mon Dec 19, 2005 5:20 pm    Post subject: Backlight Reply with quote

Hi all

I've found 2 backlight transformers and i dont know how to test if they are ok.
Which are the Backlight Capacitors? I can say the Backlight PCB is LG1504 but i can't find the schematics nor information about it.
Can you help me?

Thanx all
Back to top
Philip
Guest





PostPosted: Tue Dec 20, 2005 11:56 am    Post subject: LG LCD Model Reply with quote

I cant find the inverter cct. Ok, the inverter cct is based on some sort oscillating of push pull cct. Find the center tap of the trans'f, that is where the 12v supply is normally connected to it. The tuned cct capacitor I am refering is normally valued ard 150nF to 220nF, metalised poly type, rated about 100v.Brightness control is achieved by varying the 12v supply to it ( thru switch mode power supply).
Also check for thermal stability problems( overheating). Has the ambient temp of the backlight cct increase, brightness increase accordingly.
If all else failed, then apply a fixed voltage to the inverter cct. Voltage value depends on the brightness level required.
Good luck.
Note: refer to Fairchild Semiconductor Appl Note AN-4136 for some ideal on working of LCD backlight
Back to top
Pep Boix
Guest





PostPosted: Tue Dec 20, 2005 7:30 pm    Post subject: Txs Philip Reply with quote

Many thanx Philip,

I'll try to follow your explanations ...
but .. the Power Supply is 24 V
I'll try to learn from the APP Note you gave to me

Txs again

I'll post my news

C U all
Back to top
Display posts from previous:   
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Equipment Repairs All times are GMT
Page 1 of 1

 
Jump to:  
You can post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Електроника София - Service Manuals Free Download - Prikachi - Service Diagrams

Free TV Schematics Download - HARDW.net - Pinout Master - Jabse Search - Jabse.InK  - Pulsator

Connector Pinout Forum - Новини - SnimkiOt.com - безплатен DNS - Whois разузнаване - Poblizo.com : пътешествия