Laptop Screen Only Works at Specific Angle

[quadrant]

Why does my laptop screen only work when opened at a specific angle?

When opened at a specific angle, the screen works as expected. However if moved even slightly, it becomes non-responsive, ultimately resulting in a white screen. Finding this specific angle is an art, and one that is guaranteed to not work most of the time...

Oddly enough the webcam (which shares the display cable with the screen) works regardless of whether the screen is or isn't.

My first suspicion was that perhaps overtime, the display cable had become damaged at the point where it passes through the hinge connecting the top half of the laptop (display) with the bottom half (keyboard etc.).

So I opened up the laptop and took a closer look at the display cable. More specifically, I opened up the display cable at the section which goes through the hinge up to the motherboard. Unfortunately (or fortunately) I did not see anything to confirm this theory. All the little wires were intact, with no visible stretching, tears, etc.

I also gently tugged at each wire to check if maybe it had become loose from the black housing (connector). However, each one seemed to be in place, none were dangling loose...

I also did a visual check of the connector on the motherboard and saw no obvious solder joint problems.

I have gone to great lengths to ensure that the connections between 1) the display cable and LCD and 2) the display cable and motherboard are as tight as possible. A loose connection is unlikely to be the problem...

What do you think is the problem here?? What is typically the problem in this situations?? 

[quadrant]

Below are more images for context. Please ignore the masking tape in some.

[TheMG]

You need a new cable.

Sometimes the wires themselves will break, even if the insulation on the outside looks perfectly intact. This is due to metal fatigue from the wires bending and twisting each time the display is opened and closed.

As for the webcam, even if it shares the same cable it will have dedicated pins/wires as it is likely a USB device. The display connector would be most likely some form of LVDS signalling and power.

It only takes one bad wire out of the entire cable to really mess up the functionality of the display.

[andy3055]

The comment above is correct. However, if you check the wires end to end with a meter, you should be able to find the broken one. That being said, some of the "good" ones will break soon as they have gone through the same open/close cycles.

[shakalnokturn]

Usually the LVDS cable as said by others.
FWIW I recently had a case on an old laptop where I was pretty sure the LVDS cable was bad as I had your typical symptoms. It turned out to be a bad contact in the LCD itself. (Top left COF.)

[quadrant]

Thank you everyone for taking the time to reply!

Sometimes the wires themselves will break, even if the insulation on the outside looks perfectly intact.

Ohhh, I see.

However, if you check the wires end to end with a meter, you should be able to find the broken one. That being said, some of the "good" ones will break soon as they have gone through the same open/close cycles.

Testing the wires end-to-end proved too challenging without cutting the wire... The LCD connector in the cable has many pins packed very closely together (difficult to probe). And without a schematic, it's hard to know which pin goes to which wire, unless I fully unravel the cable.

It turned out to be a bad contact in the LCD itself. (Top left COF.)

Wow, how did you finally diagnose that? Did you attempt to do the repair yourself, or did you opt to just buy a new screen?

---

Guess this one isn't an easy DIY repair. 

Are there any suggestions for things I can do to prevent a new display cable from suffering the same fate as this one? Maybe reinforce the cable (at the hinge section) with masking tape??

[JKKDev]

If you want to test the cable you can start at the display side. The displays in most cases have a standard pinout.

1) Count the number of pins. It's either 30 or 40.
2) On the connector locate 2 sets of 3 pins (in a group) that are connected together (as in all 3 are on the same trace). There might be 3 sets.
3) One set should be connected to ground and another should be at ~17V (in my case the 17V was present even if the laptop was off, the cable has to be connected ofc). If there's a 3rd set it should have 3.3V only when the laptop is on.
4) Search for a 30/40 pin LVDS pinout with the power rails located at the pins you found them on.
5) All the other signals should correspond to the pinout (look at ground pins between LVDS lines etc.)
6) At this point you can probe for voltages at the display. I would guess one of the LVDS lines is broken.
7) Replace the broken cable. Job done

[ucanel]

New cables are not expensive, it absolutely worth to try.
I have the same problem over 2 years now.
But mine has a little bit  more angle that the screen works and
i am using that laptop always at the same place
so it does not bother me.
For testing the cable
when laptop is working i played with the cable especially
at the hinge place and screen comes and goes.
You may cut and reconnect the cable also.
I will try this if it goes worse than this.
Mine over 10 years old and i used it very bery harshly
it dropped from 2  meters at least 3 times.
And its some of the keys at the keyboard started to not working occasionally, one of the ram got broken...

[quadrant]

I searched a bit harder and was able to find the schematics for the:

• LCD display
• Motherboard display connector
• Motherboard display controller?

With this, I was able to take a guess at the pin mapping. (Let me know if anything is obviously wrong).



When I get a chance to open up the laptop again, I'll test the wires accordingly. It would be really nice if I can manage to repair the cable. Getting a "new" replacement cable, while possible now, will likely become more and more difficult as the computer "ages".

[quadrant]

But mine has a little bit  more angle that the screen works and
i am using that laptop always at the same place
so it does not bother me.

I think from now on, I'll try to minimize the number of times I open and close a laptop's screen. It's too bad the manufacturer overlooked this sort of IMPORTANT aspect of a laptop's daily use.

[TheMG]

What's the model of the laptop and how old is it?

It's entirely possible the cable had a defect in it to begin with, and the replacement will last much longer. Who knows.

[andy3055]

"Testing the wires end-to-end proved too challenging without cutting the wire... The LCD connector in the cable has many pins packed very closely together (difficult to probe). And without a schematic, it's hard to know which pin goes to which wire, unless I fully unravel the cable."

It can be done. Use two pins to prick through the insulation at each end and hook them to the meter. then flex the wire at the point where it has the bend. Once you have an idea which one is broken, flex/pull it apart at that point. a wire with a broken inside will flex easily and also when pulled apart, you will see the insulation getting thinner at the broken point. This is how I have done it. It does take time and if you cannot get a replacement, this i the only way to find the break.

[shakalnokturn]

It turned out to be a bad contact in the LCD itself. (Top left COF.)

Wow, how did you finally diagnose that? Did you attempt to do the repair yourself, or did you opt to just buy a new screen?

I ended up running it with the plastic covers off the screen, initially to check connectors at that end of the LVDS.
Various twisting / poking actions narrowed it down to one corner of the screen.
I was seeing to the case for a friend, I don't charge friends, I didn't have a spare LCD of that model in the stash so it ended up as neither a fix nor a replacement:
I lifted the PCB and put a soft wedge in the inner bend of that COF, reassembled, twisted and tapped like mad to check it was behaving.
Returned it to my friend explaining that next time the screen would need replacing.

[quadrant]

It's entirely possible the cable had a defect in it to begin with

The laptop is a HP Pavilion. That would be the best case scenario. Only time will tell how the new one fares out.

Use two pins to prick through the insulation...

That's a neat trick! Thanks for sharing.

@shakalnokturn
I see, glad you managed to find a workaround!

[ucanel]

I think from now on, I'll try to minimize the number of times I open and close a laptop's screen. It's too bad the manufacturer overlooked this sort of IMPORTANT aspect of a laptop's daily use.

Yes that is one of the first problems may arise with the age of the laptops but
i do not think it is a design flaw because
2 or 3 years of usability is enough as a laptop lifespan
after that we as a consumer need to be able to buy a new one.

[Gyro]

Pah! I don't even start looking at laptops until they're older than that and have plenty of cheap spares on ebay. Mind you, I then buy decent solidly built ones with lots of I/O, normally Lenovo T series.

[quadrant]

Update

The new display cable arrived and I finally got around to opening up the laptop again.


Results:

1) The screen behaved the same way with the new cable 

2) I tested the old cable for broken wires, and found none!*
There is the possibility that when I tested the cable, I held it in that sweet spot where all broken wires made contact to provide continuity. However, given that the screen behaved the same way with the new cable as it did with the old one, I suspect the problem is not with the display cable.

3) When I inspected the connector on the motherboard, I did not see any visible signs of lifted pins. However, I did notice that on the other side of the board, directly beneath the connector, is the copper pipe from the heatsink... Maybe thermal voodo has caused the solder joints to fail at a microscopic level.


Steps forward:

I do not currently have the tools on hand needed to rework the connector. (The pitch is too small, and there are super tiny components right next to it). Also, reworking the connector would probably necessitate removing the CPU (to get rid of the large copper heatsink directly underneath the connector). Reworking the connector is currently more effort than I'm willing to put in at the moment.


*Inspired by @andy3055's comment, I used a needle to help me probe the smaller of the two connectors. (Thankfully my probes could reliably contact the bigger of the two, so less work).

[shakalnokturn]

You should be able to find out if the problem is in the LCD or mainboard by some extensive prodding.

[andy3055]

If the cable is good and the display works when you adjust it, check the cable end that connects to the back of the display. May be there is a poor connection on that end on the connector on the display itself.

[jackthomson43]

Yeah, clearly an issue of faulty cable jack, when you move your screen, the jack got disconnected and thus LCD 16x2 display fades off and when jack is in its proper location, LCD works fine !!!

[quadrant]

If the cable is good and the display works when you adjust it, check the cable end that connects to the back of the display. May be there is a poor connection on that end on the connector on the display itself.

I doubt this is the issue. The last time I opened the laptop, I added a generous amount of tape to hold down the connector to the LCD screen. When I opened up the laptop again, I checked to see if the connector was still seated, and it hadn't budged.

Yeah, clearly an issue of faulty cable jack, when you move your screen, the jack got disconnected and thus LCD display fades off and when jack is in its proper location, LCD works fine !!!

I've tested the laptop with both connectors visible (exposed motherboard, no backshell on the LCD) and saw nothing indicating a connector coming loose...

[aqibi2000]

Firstly testing an intermittent connection using an ohm meter is not the right way to it, you do understand some of these LVDS signals are over 10MHz so if your cable moved momentarily for say 10us during your measurement went open circuit your ohm meter would not detect it (by you moving the cable around). But at the operating speed when the unit is powered on at the say 10MHz a few missed clock cycles could easily cause a blank screen.


Secondly the issue is intermittent so your  basic visual  inspection of  the connector to see if something loose is completely and utterly useless.
If it is defective, it would have a hairline crack (difficult to see cold solder joint) require at least a x40 magnification microscope  to even come close to seeing the fracture consding the pitch of a 30-40 pin LVDS connector’s SMD pad.

Go back find the fault.

If you have some electronics tools, inject a small voltage into the pin and measuring on the otherwise with the oscilloscope whilst performing the same “opening and closing type cable movement” would facilitate locating the issue of when a signal is lost or degraded

Or reflow BOTH connector joints with good flux. I don’t presume the screen’s Hall effect sensor is involved.

Rant over

[flolic]

From my experience, problem is VERY rarely in display cable, and when the cable is bad it is almost every time broken naked GND wires. Those wires are thicker than the signal ones and will always fail first.
Intermittent problems are very often caused by bad LCD panels, especially on slim variants.
 

[aqibi2000]

From my experience, problem is VERY rarely in display cable, and when the cable is bad it is almost every time broken naked GND wires. Those wires are thicker than the signal ones and will always fail first.
Intermittent problems are very often caused by bad LCD panels, especially on slim variants.
 

The issue is going to be the connector, he’s opted replaced the cable already btw