View previous topic :: View next topic |
Author |
Message |
Pep Boix Guest
|
Posted: Tue Dec 13, 2005 4:40 pm Post subject: LG LCD 575MS problem with brightness |
|
|
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
|
Posted: Tue Dec 13, 2005 10:16 pm Post subject: Seems is finally down |
|
|
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
|
Posted: Wed Dec 14, 2005 9:04 am Post subject: LG Flatron |
|
|
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
|
Posted: Wed Dec 14, 2005 3:45 pm Post subject: LG Backlight Panel |
|
|
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
|
Posted: Mon Dec 19, 2005 5:20 pm Post subject: Backlight |
|
|
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
|
Posted: Tue Dec 20, 2005 11:56 am Post subject: LG LCD Model |
|
|
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
|
Posted: Tue Dec 20, 2005 7:30 pm Post subject: Txs Philip |
|
|
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 |
|
|
|
|
|
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
|
eServiceInfo on FB -
Service Manuals Free Download -
Service Diagrams
Free TV Schematics Download -
HARDW.net -
Pinout Master -
Jabse Service Manual Search -
Jabse.InK -
onTap.bg
SnimkiOt.com -
Poblizo.com : пътешествия
Latest Service Manuals :
21NI60 02 Erisson • FT-7B Schematic YAESU • Panel CMO N173O6-L01 0 [DS] . Various • GLP23A TX-26LE8F TX-26LE8FS TX-26LE8L TX • 2sb1192 Inchange Semiconductor • E3633A and E3634A DC Power Supplies Serv • 2sa940 LGE • 2sa1263 Toshiba • KCD-139 Kenwood Radio CD • Installing-Heat-Shield-2 apple •
|