Jumping Display Problem - Dell 5520

[caspian]

Dear Forum Members,

I have got a Dell Inspiron 5520 laptop that works fine except for its display.

During every 4-second internal, the followings happen:

- At the start of the first 2-second sub-interval, the display immediately moves up by 3 millimeters. This move is due to the fact that the rows on the first 3 millimeters of the display disappear so that the other rows of the display move up. I illustrated this in the attached video.
- Then, the display stays at that position during the first 2-second sub-interval.
- At the start of the second 2-second sub-interval, the display immediately moves down to its original position. This move is due to the fact that the rows on the first 3 millimeters of the display appear again.
- Then, the display stays at that position during the second 2-second sub-interval.

Then, all of these are repeated for the next 4 seconds too and so forth.

The backlight is fixed at its position. It does not move. The problem is the same in Bios and in Windows with/without HDD. The jumping display is not distorted or bad except for the rows on the first 3 millimeters. The display is OK without jumping on external monitor.
I do not have another Screen/Cable to test. the laptop does not have a dedicated Graphics chip.

What do you think is defective: Screen, LVDS Cable, Bios, or Mainboard?
Why do the rows on the first 3 millimeters of the display disappear regularly at a constant frequency?

Thanks

[KvnTM]

Re: Jumping Display Problem - Dell 5520

I'd vote for a bad lcd.
Bios can't be the cause because it has nothing to do with the image generation.
Mainboard is also most likely not at fault since external displays are fine.
A broken LVDS cable won't produce such issues at a constant interval. It would be much more sporadic and/or show a corrupted/distorted image.
Also there is no signal with a 2 second interval which would trigger this.

My guess would be a row driver on the lcd itself which fails when heating up and start working again when cooling down. This would explain the somewhat fixed interval. Can you apply a little pressure on the borders of the lcd? If the behavior changes you got your culprit. Dont apply to much force our you might crack the lcd.

Also a failing row driver would explain the pixels going white in the affected area. Pixels are usually "open" when no voltage is applied to them. At least i always had that behavior when only enabling the backlight without powering the lcd itself.

Dont really know what else would show a failure like this. pretty odd to be honest.

[caspian]

Re: Jumping Display Problem - Dell 5520

thanks
I applied pressure on all sides of the screen and also on the LVDS cable, but nothing changed. Even the frequency of the jumping display stays approximately constant and no distortion appear.
Since the frequency is constant, I think some clock-synchronized signal is malfunctioning. But I am not familiar with components on the LCD board. So I need guidance on what component on the LCD board to test or replace.
I do not know which component on the LCD board is able to delete the first rows of the picture matrix. Is that the TCON IC? Is it possible to replace it?

[KvnTM]

Re: Jumping Display Problem - Dell 5520

LCDs are driven in a matrix by row and column drivers. They are much like shift registers and if one fails you get either a dead horizontal or vertical line.

I didnt find any good pictures as an example but this will do:

On the picture are 4 row drivers at the bottom and 2 column drivers on the right.
There are usually a lot more of those drivers on lcd's. This is just for illustration.

The board on the lcd doesn't have much components. Most likely only one tqfp which splits up the lvds data and buck/boost converters for lcd voltages. You could get in there with an oscilloscope and look for any signal with a 2 second interval. Should be fairly quick because all drivers are multiplexed and there aren't many pins.

Getting datasheets for any chip on lcd's is very hard since these are usually custom chips made for the panel.

[caspian]

Re: Jumping Display Problem - Dell 5520

thanks again, Do you mean the TCON IC for tqfp?
Is it possible to replace it?
Is there any clock generator IC on the screen board that may be malfunctioning and may cause this jumping display?

the screen model is: B156XTN02.0 , H/W: 0A , F/W: 1

[KvnTM]

Re: Jumping Display Problem - Dell 5520

thanks again, Do you mean the TCON IC for tqfp?
Is it possible to replace it?
Is there any clock generator IC on the screen board that may be malfunctioning and may cause this jumping display?

the screen model is: B156XTN02.0 , H/W: 0A , F/W: 1

Yeah there is one main chip on the board which is the tcon ic. Usually it is the biggest one in a qfp or tqfp package. Should be replaceable if you find one. The others are just housekeeping stuff and power management.
Not really sure if there are any clock generators on it since pixel clock, hsync & vsync are driven by the GPU over LVDS. There is probably a crystal or rc resonator for the tcon chip but i doubt that's the issue here.

One thing that is odd is that the whole picture seems to jump up and down. A failing row/column driver would usually result in a dead horizontal or vertical line on the screen without affecting the rest of the image.

Seems more like a timing issue but your guess is as good as mine. Do you have any other panel to test on that board? Would be nice to know if the panel is faulty or something on your board. Never seen something like this.

[caspian]

Re: Jumping Display Problem - Dell 5520

I will report here if I find another panel to test. thanks.
Pixels on the first rows of the screen are ok. Only the first rows of the picture disappear and appear again. I never faced such problem neither.

[caspian]

Re: Jumping Display Problem - Dell 5520

any confirmation or more ideas on this jumping picture, please?

[KvnTM]

Re: Jumping Display Problem - Dell 5520

I will report here if I find another panel to test. thanks.
Pixels on the first rows of the screen are ok. Only the first rows of the picture disappear and appear again. I never faced such problem neither.

So the whole image isn't jumping up and down like you illustrated in the short video?
The row just appears and disappears again? That would confirm my theory of a failing column driver.

If this is worth for you to try:
disassemble the lcd until you can see the flex cables that go to the panel (glass). They have a wide and narrow die on them. One on each flex. Those are the row/column drivers.
Poke them really carefully and put some cold spray on each of them while looking if the behavior changes. If so then you got your answer. But be careful with those. The traces are so fine you can't even see them without a microscope and you can imagine how easy it is to rip the die bond. There are hundreds of traces on each flex.

I guess no one encountered such an issue. It is really uncommon and even i had never seen something like this. I only had a tv which had a dead row driver which created a permanent white row on the lcd.

[mcplslg123]

Re: Jumping Display Problem - Dell 5520

@Caspian, its screen problem for sure