Samsung LE46A55 bright white screen

[bootlegger17]

Hi All,
I recently acquired a faulty Samsung LCD screen model LE46A55
It came with a strange fault whereby the left hand side of the screen when powered on from cold would appear dark and the image seemed to ghost. The darkness and ghosting would fade the longer the TV was left on, and would eventually dissappear. The darkness however seemed to be getting worse day by day and moved further into the center of the screen. My previous searches led me to suspect the TCon so I replaced this, but it made no difference. The only other tip I could find was to "twist" the frame of screen from one corner to the other. After some experiments, it would have appeared to work, and be related to the bottom left (as you look at the screen) that fixed the screen instantly when you tiwst/jiggle it a little.
This then makes me think its not a power board issue.
Knowing the a Plasma screen requires an X and Y board for doing horizontal and vertical banding I wondered if the LCD had anything similair.
I pulled the WHOLE thing apart and removed the screen from the bezel and the top metal framework off the screen only to find there is only the top connections to the LCD from the tcon connection (just like you would expect from a laptop LCD), there were no connections on the left or right hand side of the screen that could be loose. I re-assembled and prayed that maybe just maybe by dismantling and re-assembling, that it may work now.
To my dismay, it seems a different fault is now prevalent.
My screen in very bright, which makes things nigh on impossible to see.
I can just about navigate the on screen menu, but there appears to be nothing wrong in the colour setup - contrast 95/100 but brightness at 50. Tried adjusting contrast and brightness but makes little difference. Brightness only seems to affect after getting between 80-100. Anything less doesnt seem to get any darker. I tried the reset feature in the colour menu, but this made no difference.

Any ideas.
I know there is a service menu, I can try going into that, but what should I be looking for (thats if I can see it )

Regards
Jason

[sordids999]

Re: Samsung LE46A55 bright white screen

normally twisting the frame of the tv and this temporary fixes the fault could be a tab bond fault but a picture of the fault would help more

[budm]

Re: Samsung LE46A55 bright white screen

It sounds like tab bonding fault if you can flex the screen to make it works.
You can also try reseating the cables between the LCD panel and the T-CON board.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

Thanks guys.
My immediate problem now as I mentioned is that the screen is washed out. The whole screen is washed out, even from cold.
If I could rectify this issue first, I wonder whether the original issue would return.
I have reseated the tcon connection cables several times but this has no effect.

Here is a screen shot of the washed out screen.

Regards
Jason

[Shinju]

Re: Samsung LE46A55 bright white screen

Photo of the T-con? Is it an AUO optronics?

[bootlegger17]

Re: Samsung LE46A55 bright white screen

Erri yes it is. This is the replacement I bought which made no difference.
Same fault existed when using both. (that is the orginal fault with the faded black left hand side). I have tried exchanging boards since the white screen fault. Why do you ask?
J

[tom66]

Re: Samsung LE46A55 bright white screen

Very common fault on these, bet you've been sold a bad board. Top right corner there is an array of test points usually labelled VGAMA1..22 (or VG1, VGAM1, VGA1, GAMA1, etc.)

Please install the board & measure voltage on each test pad with a digital multimter (red probe on the point, black on the chassis.) Tell us the reading on every pad. Some may be missing on some T-cons so just post what you can find.

[Shinju]

Re: Samsung LE46A55 bright white screen

I am going to bet its a bad AS-15 gamma chip. I have a 37" Sammy with a Chunghwa 1370WA03C04G AUO optronics T-con with a Bad AS-15 chip that is doing a solid white screen with very very faint picture that can be seen.

As tom has instructed you, take those gamma voltages.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

Hi Tom66,

I have tested both TCons and both produce the same white screen result. Prior to me dismantling the whole lcd frame both produced equally good working results except for the original dull on left hand side fault from cold.
I really believe its something I have done in dismantling that has caused this current fault, but i have reseated everything a couple of times over and tapped around at various places but nothing makes a difference.
Could it all be down to what I suspect the original fault was - a faulty tab on the LCD. Would this be a manifestation of if the first tab (which i am now assuming creates the gamma/bright output) being at fault, and nothing else?

My test results for dc-v are:
VGMA22 0.27
VGMA21 0.50
VGMA20 0.64
VGMA19 2.76
VGMA18 3.44
VGMA17 4.23
VGMA16 4.78
VGMA15 5.04
VGMA14 6.58
VGMA13 6.75
VGMA12 6.86
VGMA11 7.64
VGMA10 7.77
VGMA9 7.98
VGMA8 9.80
VGMA7 10.10
VGMA6 10.76
VGMA5 11.70
VGMA4 12.50
VGMA3 15.02
VGMA2 15.17
VGMA1 15.45
VCOM2 10.60
VGMA_REF 15.45
VCOMF2 10.53
REF_F3 0.27

There are loads more test points - should i do any others? I take it you are looking for these ones specifically because they are labelled as gamma which controls the brightness? I see they are ranging from low to high voltage so I am guessing this is correct - is this a voltage range for the backlight that can be switched dependent on the required backlight?

Regards
Jason

[nomoresonys]

Re: Samsung LE46A55 bright white screen

wonder if it has anything to do with the inverter?, if it has separate inverter, maybe see if theres a fuse to check.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

bump

[budm]

Re: Samsung LE46A55 bright white screen

What do you get if you one one ribbon between the T-CON and the LCD panel connected one at a time?
Inverter is fine otherwise you will not have backlights.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

@budm,
If I remove the extreme left or right, I loose the associated half the screen.
If I remove the inner tabs, I get bars down the screen, almost like a self test of grey bars maybe?

[budm]

Re: Samsung LE46A55 bright white screen

What I was looking for is to find out if you at least get good picture on part of the screen when one cable is connected one at time.
At this point you may have to try a new T-CON board.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

Picture was exactly the same - over exposed - very bright white.
I have tried a different board also, with same results. The white screen only occurred after I pulled the whole TV apart whilst trying to diagnose a different fault. I believe the bright white screen it is something I have caused inadvertantly, but I dont know what.

[bootlegger17]

Re: Samsung LE46A55 bright white screen

I have since tried removing the power cable from the top of power board to the back left inverter - the screen stayed black. I have tried removing the power cable from the bottom of the power board to the back left inverter and the screen came on bright white but with darkening to the left, the went off. I repeated the same last step for the right inverter and same result. Connected all cables back up, and result still the same, over exposed white screen.
I have removed the metal frame work from the LCD and touched all tabs whilst screen is on to see if I can make any response(flickering, dimming etc), but nothing happened.
Any other ideas on why the screen is so bright?

Regards
Jason

[bootlegger17]

Re: Samsung LE46A55 bright white screen

I just found this post on badcaps;
https://www.badcaps.net/forum/showthread.php?t=31725
The pictures show exactly the same fault as mine, and the fix was the gamma chip replacement on the tcon by the looks of it. Guess I will have to investigate this avenue. Cant believe that I have two dead tcon boards though.

So which chip on my tcon board is this mysterious AS-15 Gamma chip? Is it really worth me attempting to replace the chip, or simply take another punt on another tcon board off ebay? Would there likely be any other components along with this chip that have failed - is it something else that is killing this chip, like overvoltage from the power board maybe?

Regards
Jason

[bootlegger17]

Re: Samsung LE46A55 bright white screen

I took a punt and ordered some replacement AS15-F chips to replace on the tcon board.
I have replaced but there is no difference

Here are some pics of the process.
original_1.jpg pic of original chip before removal
original_removed_1.jpg - pic of chip removed
new_infra_1.jpg - pic of chip being resoldered in my infrared station
new_insitu_1.jpg - pic of chip after replacement.

Now I have a fair confidence factor that its not the tcon board at fault, or if so, its not the chip. What else should I be looking for......

help......

Jason

[budm]

Re: Samsung LE46A55 bright white screen

So the GAMMA Voltages still show the same as in post 9?

[bootlegger17]

Re: Samsung LE46A55 bright white screen

I havent re-checked, but figured as the result is exactly the same, its unlikely to be the chip. I have not had any feedback about those values from post 9 whether they are correct or not. As the seem to conform to a sequential step up in voltage I am speculating that is how it is supposed to be, but please tell me if I am wrong here.
I can re-test the points again, but wont get chance to do that till tomorrow now.