How to perform panel test on Samsung UE70TU7020K

[learnmore]

Hello Community,

As part of an ongoing learning project, I'm trying to perfrom a panel test (where, according to some, you jump 12v to the (Tcon) then jump 3.3V to panel test pin on the FPC connector). For the model I'm testing with, I'm unsure of where the test pin is located (providing there is one). So, I'm after some help to locate it. Here are some shots of the board (note mainboard, Tcon combo board).

[viking6791]

See atached picture or folow this link https://www.badcaps.net/forum/troubl...ines-on-screen

[viking6791]

See atached picture or folow this link https://www.badcaps.net/forum/troubl...ines-on-screen

[learnmore]

Thanks viking, I had a look at your post. It's def a panel issue for me. In the post you signposted me to you tell the OP to remove and mask to Clk signals from the board bridging ribbon cable. I know from experience this works. However, for me, it's always been trial and error and checking the image. How can you exactly track the Clk signals to the specific points on the ribbon to mask in your example? I see some cut the signals, but I like the idea of tape that can be moved and removed.

[viking6791]

Hi learnmore, on this forum there are many discussions about the TV series Samsung TU, Qled and others that have problems with the display.
Take a photo of the two boards where the two ribbons are connected and post them here. I will guide you what to do after I see the two pictures.

Regards!

[learnmore]

Thanks, photos are here: https://www.badcaps.net/forum/troubl...on-a-bad-panel

Like I said, got mine to work but look so learn how to block lines with precision rather than trial and error

[viking6791]

You will find these signals on both sides of the display, if you do the jumper test at Tcon, disconnect the ribbon from each side one by one and you will have an image only on the side without a defect. Usually with this type of display as in the attached photo, I check with the measuring device on the resistance field those data and voltage lines one by one, the resistance between any line must not be less than hundreds of k ohms. The test can also be done in tension, but there are no values given by the manufacturer for this, everything depends on how much experience you have and intuition. Start by isolating the VGH voltage in the faulty part and see what reaction you get. I have also isolated some CK signals but it is not a rule which of them has problems and generally on the right side as you look from the back of the device.

[learnmore]

Thanks for the prompt reply, appreciated! I'll certainly give it a go

[viking6791]

In the last 2 months I repaired several devices from the MU, TU and Qled series, all of them were in boot loop with or without the Tizen logo, but I was too lazy or selfish and didn't take pictures of what I did, now I'm sorry because I could help more easily with the respective images.
But now I received for repair a Samsung model 40NU7100 I think, single chassis, which has vertical stripes and after 30-60 minutes it enters the boot loop. I will take pictures of the defect and the steps followed for troubleshooting.

Best regards!

[learnmore]

I (and I imagine others) would welcome that--thanks for the thought. I'll keep an eye out but if it's not too much hassle to ping me when you post it.

[viking6791]

I will post here to, and I will send you an PM also.

[learnmore]

Great, I saw in you other post you mentioned gaining some knowledge from YT but a lot from books. Anything you would recommend? I'm especially keen to learn more about panel 'repairs' and EMMc/EEPROM reprogramming.

[Donny2derby]

Yep I’d be interested in reading about that too! Any advice from anyone would be great.

[EazyBone]

In the last 2 months I repaired several devices from the MU, TU and Qled series, all of them were in boot loop with or without the Tizen logo, but I was too lazy or selfish and didn't take pictures of what I did, now I'm sorry because I could help more easily with the respective images.
But now I received for repair a Samsung model 40NU7100 I think, single chassis, which has vertical stripes and after 30-60 minutes it enters the boot loop. I will take pictures of the defect and the steps followed for troubleshooting.

Best regards!

Yes I think I am extremely interested in this. I find like 1-2 of these a week and well they basically seem like trash because I don't know the fix or the data on how to fix. I currently have a nu6900 sitting because I don't even know what to do to fix it, so I was going to transfer a good screen from where else to it or who knows. But the data of this would be amazing

[Donny2derby]

viking6791 Your loyal servants kindly request you provide us with your wisdom 😁

[viking6791]

viking6791 Your loyal servants kindly request you provide us with your wisdom 😁

Hello My friend, it is not my wisdom, it is the result of the work of everyone in this forum, I just paid close attention to these discussions and learned.
I am back with some information.

I received the following Samsung model for repair:
UE50AU8072
Mainboard BN41-02844D
Panel CY-SA050HGPY1V

The device was in boot loop without Tizen logo, the motherboard only has a ribbon that connects to the panel and that bridge between the two parts of the panel.
I did the panel test with only the left side connected and noticed those stripes on the image.
With the device turned off, I measured the resistance of those signal/voltage lines on both sides of the panel, so I decided to cut the VGH voltage on the right side (if the VGH is cut on the right side, you will no longer have an image)
and I connected that flex cable between the two sides of the screen. I turned on the device (the Tcon test is still active, that strap) and I had an image on the entire screen.
I removed the strap after turning off the device and left it for 2 hours in the test on an HD image and no problem appeared. I am attaching the pictures taken by me yesterday.
I was lucky this time too and found the defect relatively quickly.😉

P.S. I received another Samsung UE50TU8070 with the same defect, boot loop without Tizen logo.

[Donny2derby]

I keep seeing this VGH reference on various threads. What is it and what does it do? What do we test for at it?

Thanks.

[lotas]

VGH = VON = VGON = VDDG = 20 to 30 V.
VGH is the positive supply voltage for the high-voltage driver outputs CKV_, CKVB_ and STVP.
This voltage VGH (VGate High) was created by DC and AC circuits. Their voltage is around 20~30V, but this will depend on the design of the T-con board. The function of the VGH voltage is to supply the gate driver board as a "turn-on" function.

[Donny2derby]

Ahh brilliant Lotas. Thanks. So it’s a source voltage for a transistor gate??

And if we don’t have VGH we will never get an image on screen??

Are there common reasons for not having VGH? For instance a failed IC?

[lotas]

VGH and VGL production mode by the TCON board. The charge pump converter.

https://www.youtube.com/watch?v=YJyURYOUVh4&t=5s


https://www.youtube.com/watch?v=izd7dhtmZjc

[Donny2derby]

Appreciate you sending that link Lotas. But most of it went way over my head. That guy speaks so fast I wasn’t capable of taking all the information in.

But essentially when faced with a blank screen it’s good to test for VGH & VGL to determine if the T-con board is sending signal to panel drivers??