LCD LVDS is universal?

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LCD LVDS is universal?

Postby jongscx » December 10th, 2013, 10:14 am

Hey, ok so question about laptop LVDS protocol/connection.

I had an Asus 15.6" laptop and my buddy's Sager. 17" laptop screen. I was curious, so I disassembled the displays and the cable off of my laptop fit his LCD... O_O
I booted my laptop and the backlight went on but no image. The screen itself was dark.

So, I guess my question was whether those connections are universal or if I just had a happy accident with the backlight. (Both are LED backlit)

I read somewhere about how smaller LCDs signal at 3.3V and the larger ones at 5V, but haven't found anything specific.
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Re: LCD LVDS is universal?

Postby st2000 » December 10th, 2013, 9:17 pm

@jongscx, if modder_mike doesn't pick up on this thread you might try to send him a private message. He seems to have done the most w/LCD screens.

My guess is that the resolution is set wrong. Not sure if that will result in a completely blank screen. But you might try it.

Not sure it is a safe bet that all LCD back lit screens are the same. It would stand to reason that a larger screen would take more current to run.

I think some (usually smaller) screens are TTL level. But other's, (I think) especially the bigger screens are Low Voltage Differential Signal.
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Re: LCD LVDS is universal?

Postby modder_mike » December 12th, 2013, 9:50 pm

Ohai! :)

Backlight with no image, huh? Interesting. Standard TN panels are often naturally white, while IPS panels are usually naturally black. My first thought was that you weren't hitting the power pins, but (unless it's an IPS panel) a black screen would seem to indicate that it's being powered correctly.

I guess let me back up a minute. Is LVDS universal? "Sort of". Assuming you have a constant color depth and both systems use the same bit ordering, signal-wise LVDS is usually compatible between systems. There's no real "encoding" to speak of, no error correction, etc, the signal is pretty much raw - so even if the color depth and bit packing are off, you'll usually see "something", certainly not a blank screen.

What is certainly not standard is the physical interface. I have examples of more than a dozen different connector styles carrying LVDS, and inside that set I have several examples of identical connectors with vastly different pinouts. I even have an example of two otherwise identical panels, separated by only a (xx) revision suffix, with different pinouts and even completely different connectors (actually it's the LG LD070WS2 I mentioned in another recent thread). That's understandable - different OEMs may want the same type of panel, but will need the connection in a different place depending on the design of the end product - but what boggles me is when companies use the same connector in different ways on different products. For instance, Apple puts the same 30-pin I-PEX Cabline-CA connector on several of their systems but uses vastly different pinouts between them.

So, yeah. While the connector may have fit, it won't necessarily be providing the right signals to the right places. I'd venture a guess that you got lucky and the power pins were in the right places, based on the description you've given. But because the display is blank, I suspect one of a couple things. It is possible that the resolution is incorrect, as st2000 guessed, but that wouldn't be my first choice. The pixel clock rate from the resolution of a "typical" 15.6" panel shouldn't be outside the usable range of a "typical" 17" panel (unless the 15.6 is a super-high-resolution type). Even then, I'd expect the timing controller to be able to make "something" out of the signal, not just give up and shut off.

My first guess is that your clock signal is in the wrong place. No clock means the tcon will ignore any other data being presented to it. It could also be that your connectors are a pin offset from each other - as in, there's an extra pin such that pin 10 on your laptop matches the signal for pin 11 on the donor screen - which would typically result in one half of each differential pair being grounded and presumably no usable signal making it in.

Really there's a thousand different ways things could be mis-connected - the most useful thing to do would be to pull the model numbers from both panels and see if you can find datasheets for them, this will tell you the pinouts and from there you can see where things are going wrong (or post the models here and one of us can take a look as well).

Oh, and re: voltage. Yeah, a lot of times the larger panels are indeed 5V and the smaller ones 3.3V. It's no set rule, but it does make some sense: the larger panels draw more power to drive their row and column drivers (since they either have more pixels or have to twist more crystals per pixel due to increased pixel size). The wires or traces carrying signals and power to the panels are very small, so to avoid running very large numbers of wires/traces, the larger screens are delivered higher voltage which they sub-regulate onboard. But there's no rule that says "screens larger than 15 inches will be 5V" etc - it varies based on power requirements, connector type and manufacturer whim.

(extra extra aside: There is also a slim chance that one display's interface is embedded DisplayPort and the other is not, and that's why it doesn't work - because they're speaking different languages. If you have the model numbers, though, that's easy enough to rule out. It is however unlikely for them to be TTL - I will make a bold statement and say no recently-manufactured laptop drives a raw TTL display, LVDS has far too many advantages from signal integrity/EMI/cross manufacturer compatibility/etc standpoints)
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Re: LCD LVDS is universal?

Postby jongscx » December 13th, 2013, 12:22 pm

Holy crap, that's a lot to think about. I reassembled the screens so I wouldn't lose parts, but I'll get back on it after work today.
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Re: LCD LVDS is universal?

Postby jongscx » April 7th, 2014, 3:41 pm

It's almost a full month since I last posted, and here's an update: viewtopic.php?f=2&t=4379

So the "screen upgrade" is out, since I literally toasted the larger screen; however, I do still need to replace the primary, which is a 15.6" LED Backlit LCD Panel.
Here's the pictures of the Panel:
https://www.evernote.com/shard/s35/sh/1 ... 5288d65652

The Model# of the LCD looks to be: LP156WH4 - (TL)(A1) and it's manufactured by "LGDisplay"

My questions now are:

1) Why did My Laptop (Asus K53SV) not initially work with larger LCD Panel? The Model Number of the big laptop's LCD is: HSD173PUW1-A01 and Made by Hannstar.

2) I want to upgrade my screen/convert my laptop into a tablet with a capacitive Touchscreen. How would I be able to tell if an LCD Panel I'm looking at is compatible, display-wise with my Laptop? I was going to handle the touchscreen part with a stand-alone controller, but I need to know that the image is at least going to be there.

3) If I wanted to instead downgrade to a smaller LCD panel, how do I check compatibility?
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Re: LCD LVDS is universal?

Postby modder_mike » April 7th, 2014, 9:32 pm

I thought something seemed familiar about that post. :D Too bad about the toasted panel though. At least it was only a $20 lesson and not a $200 or $2000 lesson.

The datasheet for your panel can be found here: http://files.pugetsystems.com/files/336 ... 4-TLA1.pdf . The datasheet will answer some of your questions.

1) The HannStar panel's datasheet is here: http://www.yslcd.com.tw/docs/product/HSD173PUW1-A.pdf . If you compare this to the other datasheet, you will see that most of the pins are actually quite similar between the two. However the HannStar is a dual-link LVDS panel, whereas the LG is a single-link LVDS panel. It is possible that the larger screen did not work because it was receiving no signal on its Even LVDS channel, and the timing controller interpreted this as an invalid state. Otherwise I don't know what may have been wrong. Maybe something to do with Pin 1. Maybe the laptop is locked to a specific display ID. None of this explains why it went and exploded, though - maybe it was a faulty screen to begin with?

2) To know whether an arbitrary panel is compatible, compare their datasheets. You certainly want to make sure that the connectors and pinouts match, and that the operating voltages and backlight parameters are the same (for instance, you wouldn't probably want to replace it with a panel without an onboard backlight driver, unless you want to cram another PCB into the laptop somewhere). Beyond that, it might be luck, without knowing more about the laptop. It is within the realm of possibility that the mainboard could be programmed to work with only one display resolution or even only one panel (identified via EDID). It's hard to tell, especially given the evidence presented of what happened to the last display swap you attempted... If you want to see if it's panel-locked, you can try rewriting your native panel's EEPROM (after backing it up of course!) to insert new panel identification information - if it still works with a different ID, that's a good start. Be sure not to overwrite the timing information!

3) See (2).

I'm sorry I can't be more helpful... I have more experience working with universal display controllers and panels than I do in trying to make a commercial device talk to an arbitrary panel, so I can only speculate on what's possible.
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Re: LCD LVDS is universal?

Postby st2000 » April 7th, 2014, 9:53 pm

I think this conversion is going to be tough. And not only because bare LCD interfaces are far from standard.
convert my laptop into a tablet with a capacitive Touchscreen. ... I was going to handle the touchscreen part with a stand-alone controller

Exactly how are you going to do this? Are you using Windows8? I'm honestly not sure how to go about this my self. A capacitive or resistive touch screen represents an absolute positioning device. Windows8 must know how to handle this as it uses a touch screen. But earlier versions may not. (A mouse is a relative positioning device which is much different.)

Edit: added later...

Well I guess you can use a touch screen w/older windows like windows7:
http://windows.microsoft.com/en-us/windows7/products/features/touch

Can't help but notice that even though the web page and text is about windows7 the video sure does look a lot like windows8. Go figure.
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Re: LCD LVDS is universal?

Postby jongscx » April 7th, 2014, 10:34 pm

The Panel toasted because I plugged in an LED Backlit panel to a laptop which ran a CFL backlight and i'm assuming the supply was connected to the 40-pin.

The Conversion was thought up on the assumption that capacitive touch panels were just stock LCD panels that had a capacitive panel glued to their face. I had grafted a resistive panel into an Asus EEE-701 (yeah, remember those...) back in the early 2000s and it was a simple matter of routing the touch wires to a separate "touch controller" that interfaced via USB.

My understanding of the drivers was that there is an HID class for touchscreen that does absolute positioning, but this was back in XP and things might have changed.

I didn't even think to look at the actual panel data-sheets, and this is a great spring-board for further study. The laptop itself is still somewhat current which is why I've been hoping to actually save it instead of shelling out for another.

Thanks again!
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Re: LCD LVDS is universal?

Postby jongscx » April 9th, 2014, 5:40 pm

Ok, Update:

I may have found a good candidate. There are a lot of Ebay posts for the LP156WH4 - TLB1 touchscreen for a little under $100. My current LCD is the LP156WH4 - TLA1

I found the website: http://www.PaneLook.com which carries a lot of datasheets and info on these LCD Panels. From what I'm seeing, the TLA1 and the TLB1 are identical.

Mine: http://www.panelook.com/LP156WH4-TLA1_L ... 12272.html

Replacement: http://www.panelook.com/LP156WH4-TLB1_L ... 12273.html

Now I have found the datasheet for the TLA1, but not the TLB1. Is it just a newer HW revision... These naming conventions aren't really universal. >.<

EDIT: I searched for KN38A-40S-0.5H , which was the "Interface Model" and did find this datasheet: http://lcd-screen.com.ua/data/pdf/1182.pdf

It looks like it's a 10" screen, but uses the same interface model as the TLB1. Pin-wise, it is identical to the TLA1 which I got from Here: http://www.datasheet4u.com/datasheet/L/ ... G.pdf.html

Thoughts?
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Re: LCD LVDS is universal?

Postby jongscx » April 22nd, 2014, 1:21 pm

Woohoo,

Just FYI to everyone who helped, the transplant was a success and the screen is working flawlessly. Thanks for all the tips about the datasheets and matching signal pins, that was the breakthrough I had needed!

working screen.jpg
Working Screen
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