Samsung LA40F81BD Jumbled Dispaly

[Markus1]

Hi there,
That LCD TV come completely dead. Inside there were 4 swollen electrolytic caps in the secondary section of the PSU. After replacement the set came up but the screen was heavily scrambled. It settled after a minute or so and the picture was correct for quite a wile. Next day and from there on the display is jumbled for good. Below are a few photos of the screen taken on different channels (sorry for a low quality, taken by a phone).

The problem is the same on the antenna and on AV input signals. Menu screen obviously can not be shown. Audio OK. Voltages out of the PSU and into the Main Board look good too.

So, what can I check and where could be a possible problem? Is it a panel issue?
Any advice, suggestion or direction would be much appreciated.

[Hamie]

Re: Samsung LA40F81BD Jumbled Dispaly

Possibly tcon board has failed.

If you can upload a clear picture of the tcon there are several test points that will need checked.

[tom66]

Re: Samsung LA40F81BD Jumbled Dispaly

I'm gonna say bad LCD panel, try removing one ribbon at a time from the T-con and see if you get a part picture.

[newtothis]

Re: Samsung LA40F81BD Jumbled Dispaly

+1 tom66

Bad Panel

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

Thanks Hamie, tom66 and newtothis for the reply.
I did try with the ribbons on t-con, removing them one by one. Did not get a part picture. Removing ribbon 1 and 3 made half of the screen white, other 2 ribbons made no significant difference.
I accept your diagnosis for a bad panel. However, I would be very interested to learn about those test points on the t-con as mentioned by Hamie. May be helpful for the next time.
Attached below is the photo of the t-con. I appreciate your help.

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

If you can upload a clear picture of the tcon there are several test points that will need checked.

Hamie, would you be kind enough to highlight some of those tests points, please. Just for education.

[tom66]

Re: Samsung LA40F81BD Jumbled Dispaly

Have you tried all ribbon combinations?
There are four ribbons and so 16 ways they can be disconnected.
To simplify it, you can usually treat both left & right as separate, so try both left disconnected (w/ right connected) and right disconnected (w/ left connected)

Test points: Look for VONE, VOFFE, VDD, AVDD, VCC, 3V3, etc. Small gold pads with writing next to them.

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

Tried disconnecting ribbons in various combinations.
-when ribbons 1 and 2 disconnected right side of the screen goes white
-when ribbons 3 and 4 disconnected left side of the screen goes white.
Nothing really conclusive with any other variations.

Now after all these ribbon disconnections the display seems changed from what was there originally (photos in post #1). With all the ribbons in place the screen now is generally white but very pale vertical lines are still visible. These lines shift a bit as the video signal changes.

Also, found some test points on the T-con board, voltage readings are as follows:
Vin 12.5V
Vcc 3.2V
Vcc12 1.5V
Vcc25 2.5V
Vdd12 15.2V
Avddb 15.2V
I do not know what values should be expected there.

Also, checked Gamma curve voltage points 1 to 18. First half generally around 0.8 - 0.9V range. Second half mostly nothing, around 0.05V. They do not appear in any orderly sequence, certainly not increasing (or decreasing) gradually.

So, does this say anything about a bad T-con or a failed panel?

[tom66]

Re: Samsung LA40F81BD Jumbled Dispaly

Where did you find gamma voltages? Those voltages are definitely bad. Is the gamma IC getting hot? Do the voltages come back with the ribbons removed?

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

Where did you find gamma voltages? Those voltages are definitely bad. Is the gamma IC getting hot? Do the voltages come back with the ribbons removed?

See picture below, Gamma voltage test points marked in red.
(I have read about it in one of your earlier posts on this forum.)
I am not sure which IC is the Gamma IC, however none of the IC's were hot.
The voltages were measured with all ribbons in, I did not check them while the ribbons were disconnected.
Will do it again tomorrow.

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

Tom66 I took the Gamma voltage readings again, this time with all 4 ribbons disconnected.They still look bad.
1. 0.90V
2. 0.003V
3. 0.967V
4. 0.934V
5. 0.937V
6. 0.947V
7. 0.002 V
8. 0.958V
9. 0.002V
10. 0.109V
11. 0.143V
12. 0.072V
13. 0.071V
14. 0.069V
15. 0.063V
16. 0.060V
17. 0.046V
18. 0.010V
I think that the Gamma IC is the big one in the center of the board. Its has markings like that: AMLCD, LMU4148T1, B-NOWC7M, H0745

So, how do you take it now?

[tom66]

Re: Samsung LA40F81BD Jumbled Dispaly

IC18 is probably the gamma IC.
I have not seen these ones fail before.
I still think your panel could be bad so there's a fair risk that swapping the gamma IC wouldn't fix anything.

[Alastair E]

Re: Samsung LA40F81BD Jumbled Dispaly

Looks like a LCD Panel fault to me too....

[budm]

Re: Samsung LA40F81BD Jumbled Dispaly

I say bad panel.

[newtothis]

Re: Samsung LA40F81BD Jumbled Dispaly

Well that's most of the regulars saying bad panel now LOL

[Markus1]

Re: Samsung LA40F81BD Jumbled Dispaly

A big thank-you to all who responded and offered advice and opinion on the presented issue.
I accept your verdict and write this TV off. Nevertheless, it was a good learning experience.
This forum is a fantastic source of information and you guys are most generous in sharing it with the rest of us, eager to learn.
Thank you again.