lg 55ls4500 negative picture

[milleradam37]

Hello all,

i have an lg 55ls4500 that appears to have a brightness problem, when i turn the brightness up past 75, i have a decent picture, but when set on 50, which is supposed to be standard setting, i start getting a negative picture which gradually gets worse as the brightness decreases.
When i first got it, the image from other input would stay on screen forever, so i changed the main board, which seemed to help, but still had the negative image in the picture here and there , had to reall play with adjustments to get a decent picture. So now i changed the t-con board also, which made little differance.
so, of course i checked all named power supply voltages, 12,24,5 all there and the led power is 69volts. im not exactly sure what it supposed to be. the 400v is around 393v
So, where i am at is i can get a good picture with brightness around 85-90
any ideas what i am missing? i have attached 2 pics, one with bright down and other with bright up high.

[milleradam37]

Re: lg 55ls4500 negative picture

ok, after a little research it looks like the actual problem is called solarization.... the menu always appears normal so i am fairly confident that the panel is fine, but the fix is supposed to be either main or t-con board, both of which i have already changed. im thinking that i received a bad main board, thoughts? does anyone know of anything on the main board that is replaceable for this issue? i really dont want to invest any more money into this than i have to at this point

[budm]

Re: lg 55ls4500 negative picture

https://www.badcaps.net/forum/attach...6&d=1523491945
That looks like bad GAMMA Voltages which are on the T-CON board.

[maxvalutech]

Re: lg 55ls4500 negative picture

The solarization problems I have encountered have all been related to tcon boards. Do check the specific board numbers on your boards, usually the white sticker, to ensure they match the original board stickers. Then again most recent solarization problem was intermittent and was caused by poor connection lvds to tcon - not readily evident the slightest movement once set warmed up started the problem - taping appears to have fixed it after firming up connection as best I could.
Edit - just saw budm reply above , yes check the gamma voltages and note they can be hard to get to on some sets. The results have to be linear.

[milleradam37]

Re: lg 55ls4500 negative picture

ok thanks guys i will double check the part number on board, i ordered the new one from shopjimmy supposed to be a good place. so, is there a chart of gamma voltages anywhere? will those voltages change as you adjust brightness? is the brightness pwm or linear controlled?

[maxvalutech]

Re: lg 55ls4500 negative picture

There are a number of posts showing gamma test results and basically you start with say the low voltage then each one after that is a bit higher etc etc ascending in order. A problem with them is then easy enough to spot due to a disparity.

[Davi.p]

Re: lg 55ls4500 negative picture

I don't agree with TCON gamma problem and maybe nor TCON problem, for me there's something not compatible between old mainboard and new one, i suggest to go to LG support site, download the last firmware for the correct model, update it and go into service menu (this is really tricky unfortunately) and do a service reset. Maybe there's another method to reset the settings (eeprom pin short)

[maxvalutech]

Re: lg 55ls4500 negative picture

Relating to the initial post turning brightness up should normally make solarization worse. The led voltage looks low for set size and you say the brightness diminishes after selection so is that voltage going down as well from PSU ? On both main and tcon replacement boards do the stickers agree with the old boards stickers ?

[milleradam37]

Re: lg 55ls4500 negative picture

ok, found original problem== i feel pretty silly now for not looking here before, looks like along with the water damage i have corroded traces and smd resistors. i dont suppose anyone knows the values? i can make out a couple but the rest i cant make out. also has any successfully repaired similar ? i doubt i will attempt to replace the board dont have a good way to re-attach those ribbons

[diif]

Re: lg 55ls4500 negative picture

Your photos are too blurry to read the values.
Be very careful not to tear the ribbon, there is no economical way to reattach them.
If you heat one side of the resistor then the other with a ball of solder on your tip the resistor should then just wipe away.

[Davi.p]

Re: lg 55ls4500 negative picture

But the second photo is the cleaned part of that visible in photo 1?

[budm]

Re: lg 55ls4500 negative picture

I am still curious if the liquid damage on that tab bonding has effect on the GAMMA Voltage readings or not, that will be good to know that damaged tab bonding can or cannot affect GAMMA problem or not.

[milleradam37]

Re: lg 55ls4500 negative picture

Your photos are too blurry to read the values.
Be very careful not to tear the ribbon, there is no economical way to reattach them.
If you heat one side of the resistor then the other with a ball of solder on your tip the resistor should then just wipe away.

i was actually hoping someone here might by chance have one of these units and could ohm them out, when i checked them after cleaning them up i got nothing. i tried looking on the other board to see if the same resistors were there, but apparently the boards are different (l) and (r) marked on each. the damage was on the left board. i tried to find these boards for sale somewhere, but nothing yet, considering that a cracked panel would make these boards worthless unless you have some water damage like this that is still possible to repair.

[diif]

Re: lg 55ls4500 negative picture

The boards might be different but the values won't vary much.
Use a magnifying glass and compare to the other side. You have numbers written on them.

[Davi.p]

Re: lg 55ls4500 negative picture

What do you have used for cleaning? The oxid is maybe too much, i suggest you to put on them a big amount of flux and warm it until it deoxidizes, another possible method *NOT TESTED* is to dive it into a little pool with boiled water with salt, let it stay for an hour oro so, then wash it with clean water... BYE.

[milleradam37]

Re: lg 55ls4500 negative picture

Ok, so i finally got back to this 'dog' , and have successfully repaired the corroded traces and components, not pretty, but it worked! thanks for all of your input guys. i drew some of the corroded part in case anyone else needs in future. also, maybe for future reference check to see if the following are open when brightness doesnt work properly r215(smd 188 ), r216(smd 472) , r210 (smd 272) , r213, r214(smd 101) r211,r212 (smd 08A (eia-96)). c251, c250 had corrosion as well, but i couldnt find any numbers and could get a reading only about 100nf, but the set works none the less .