Author Topic: The viability of repairing modern LED backlit LCD monitors  (Read 1484 times)

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Offline WaveyDipole

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The viability of repairing modern LED backlit LCD monitors
« on: October 13, 2018, 06:50:48 pm »
I have recently had a ViewSonic VX2776 monitor fail on me. I paid £100 pre-owned only a couple of months ago which is half of what they sell for brand new. The display still works, but has started to flicker horribly (it had done this briefly a couple of times previously) and sometimes leaves faint  "after-images" of the previous image on the screen making it unuseable again until after it has been left standing for a few hours. It is definitely not the graphics card in my computer or my PC but some kind of 'memory effect' caused by the internal display controller in the monitor. Its was kind of weird to power down the display, disconnect the HDMI connector and then still see the faint afterimage of my previous screen on power-up! I am typing this using a repaired Dell  S2309WD CFL backlit display which works perfectly fine and confirms that my PC graphics card is perfectly OK.

Having just seen Dave's teardown video #465 showing what's inside one of these monitors (thanks Dave for a very interesting video), it would seem that these days there is not much in them that can be serviced inside. The power supply is via an external brick so there is no PSU board with that might have leaking caps leaking, no inverter boards that might have faulty transformers. There is just a processor chip with a scattering of few SMD components. All of this probably should make for great reliability, but clearly they do still fail. This display has no bezel to speak of and no back panel mounting screws so all glued together as one piece so the prospect of trying to prise it open seems quite risky.

Does this sadly mean that when these displays are now pretty much throw away?

If anyone has any ideas as to how it is even remotely possible to get an afterimage on one of these I would be interested to know!
 

Offline free_electron

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #1 on: October 13, 2018, 07:00:41 pm »
just because it uses an external brick doesnt mean there are no bad caps inside !
the led driver still pumps voltage up and the soc still has a switching regulator...

and .. how stable is the output of hat external brick ?
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Offline james_s

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #2 on: October 13, 2018, 07:04:35 pm »
I've repaired two different LED LCD TVs that had a bad LED that was causing the backlight to shut down. I've repaired monitors that had bad capacitors, broken joints on connectors, they're certainly fixable.
 

Online tooki

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #3 on: October 13, 2018, 08:57:46 pm »
As for the ghosting, look up LCD image latency LCD image retention. It’s a known effect in some kinds of LCD panels.
« Last Edit: October 14, 2018, 11:49:08 pm by tooki »
 

Offline Nusa

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #4 on: October 13, 2018, 11:27:48 pm »
What's the manufacture date? Is it still in the warranty period?
 

Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #5 on: October 14, 2018, 12:03:30 pm »
What's the manufacture date? Is it still in the warranty period?

That's an interesting thought. The date is stated as 2016-07-12 so just a little over 2 years. Their products carry a 3 year limited warranty so I perhaps would have a case. According to the terms of the warranty, they do require proof of purchase of  the  ViewSonic  product and I am at the present unable to find a receipt from the secondand goods shop I purchased it from. Also, the terms seems to apply to the USA and Canada only so I'm not sure what applies in the UK. Still its an avenue that might be worth pursuing since it has failed within the warranty time period. I will contact them and find out where I stand on this.

just because it uses an external brick doesnt mean there are no bad caps inside !
the led driver still pumps voltage up and the soc still has a switching regulator...

and .. how stable is the output of hat external brick ?

That's also a good point. I will have to try it using a different power supply.

As for the ghosting, look up LCD image latency. It’s a known effect in some kinds of LCD panels.

Thanks for the thought and I did search on "LCD image latency" as suggested. The references seemed to refer to the kind of ghosting where the image lags behind the audio or where action smears on the screen. However, in this case, what I actually saw was a static "imprint" of the brighter open windows on my desktop that were already open just prior to my shutting down the computer. After shutting down the computer I disconnected the HDMI connector and powered down the display, waited a few seconds and powered it up again - and without anything connected to the monitor, there it was, feint and lacking detail, but distinct enough for me to determine that there were the two windows I had opened just a two or three minutes ago. So where was this image being stored? Is there image memory in the monitor? Was it somehow being stored in the LCD panel? I wish I had taken a photo as it was surreal.

Having posted this, today just a few minutes ago, I connected the monitor up again and it seems to be working properly again. There was a very slight flicker when I turned it on, but now that it has warmed up for a few minutes, it is OK. So here again is a dilema - if I send it back under warranty, there will be a delay of a few days before it is looked at and the chances are that by the time they do it will be working fine....
« Last Edit: October 14, 2018, 12:39:45 pm by WaveyDipole »
 

Offline PointyOintment

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #6 on: October 14, 2018, 02:12:31 pm »
What's the manufacture date? Is it still in the warranty period?

That's an interesting thought. The date is stated as 2016-07-12 so just a little over 2 years. Their products carry a 3 year limited warranty so I perhaps would have a case. According to the terms of the warranty, they do require proof of purchase of  the  ViewSonic  product and I am at the present unable to find a receipt from the secondand goods shop I purchased it from. Also, the terms seems to apply to the USA and Canada only so I'm not sure what applies in the UK. Still its an avenue that might be worth pursuing since it has failed within the warranty time period. I will contact them and find out where I stand on this.
Brexit hasn't happened yet (AFAIK), and the EU has a mandatory 3-year warranty law (IIRC), so probably. Knowing the EU, it probably even covers things you got secondhand or off the curb.

However, in this case, what I actually saw was a static "imprint" of the brighter open windows on my desktop that were already open just prior to my shutting down the computer. After shutting down the computer I disconnected the HDMI connector and powered down the display, waited a few seconds and powered it up again - and without anything connected to the monitor, there it was, feint and lacking detail, but distinct enough for me to determine that there were the two windows I had opened just a two or three minutes ago. So where was this image being stored? Is there image memory in the monitor? Was it somehow being stored in the LCD panel? I wish I had taken a photo as it was surreal.
That sounds as if the panel retained its image because it stopped being driven without first being blanked (due to power loss or incorrect shutdown sequence internally). However, I don't know if that's something that happens to LCDs. EPDs do that for sure (and consider it a feature).

Offline rdl

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #7 on: October 14, 2018, 02:41:54 pm »
I had an Asus monitor that developed an intermittent LED back light fault while under warranty. I sent it in for repair at least four times but they still never managed to fix it. They were paying for FedEx shipping both ways so they almost certainly lost money. I finally got tired of packing it up and taking it to the shipper and just gave up. I bought a Benq monitor to replace it and I haven't bought another Asus product since.
 

Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #8 on: October 14, 2018, 07:20:17 pm »
However, in this case, what I actually saw was a static "imprint" of the brighter open windows on my desktop that were already open just prior to my shutting down the computer. After shutting down the computer I disconnected the HDMI connector and powered down the display, waited a few seconds and powered it up again - and without anything connected to the monitor, there it was, feint and lacking detail, but distinct enough for me to determine that there were the two windows I had opened just a two or three minutes ago. So where was this image being stored? Is there image memory in the monitor? Was it somehow being stored in the LCD panel? I wish I had taken a photo as it was surreal.
That sounds as if the panel retained its image because it stopped being driven without first being blanked (due to power loss or incorrect shutdown sequence internally). However, I don't know if that's something that happens to LCDs. EPDs do that for sure (and consider it a feature).

Possibly something along those lines might make sense. I first noticed the intermittent flicker problem during mid-summer when the monitor had been on for several hours during a really hot day. It has not happened for a while until the other day when I posted this thread, although that that day, the display had been on for several hours again. Ironic given it says 'Flicker Free' on the front! It was the first time that I noticed the issue with the after image though. I don't know enough about the LCD panel technology either to know whether it requires a blanking singnal to clear the LCD pixels although, if it is something along these lines, then it is beginning to look an intermittent joint problem.


 

Offline ebastler

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #9 on: October 14, 2018, 09:08:56 pm »
the EU has a mandatory 3-year warranty law (IIRC), so probably. Knowing the EU, it probably even covers things you got secondhand or off the curb.

The mandatory warranty is  2 years only, unfortunately. And while you don't have to be the original purchaser to benefit from the warranty, you will need to present the proof of the original purchase. (The end user's warranty claim is vs. the dealer, not the manufacturer; although manufacturers will hold dealers harmless.)
 
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Online tooki

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #10 on: October 14, 2018, 11:52:18 pm »
.
As for the ghosting, look up LCD image latency. It’s a known effect in some kinds of LCD panels.

Thanks for the thought and I did search on "LCD image latency" as suggested. The references seemed to refer to the kind of ghosting where the image lags behind the audio or where action smears on the screen. However, in this case, what I actually saw was a static "imprint" of the brighter open windows on my desktop that were already open just prior to my shutting down the computer. After shutting down the computer I disconnected the HDMI connector and powered down the display, waited a few seconds and powered it up again - and without anything connected to the monitor, there it was, feint and lacking detail, but distinct enough for me to determine that there were the two windows I had opened just a two or three minutes ago. So where was this image being stored? Is there image memory in the monitor? Was it somehow being stored in the LCD panel? I wish I had taken a photo as it was surreal.
Argh, sorry, I sent you down the wrong rabbit hole! Brain fart. The term I was thinking of was image retention (or persistence). See https://en.wikipedia.org/wiki/Image_persistence
 

Online tooki

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #11 on: October 14, 2018, 11:54:30 pm »
Use something to completely fill the screen with white for a while — and exercise it by playing video.
 

Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #12 on: October 15, 2018, 02:13:18 pm »
See https://en.wikipedia.org/wiki/Image_persistence

Yes, that looks like the effect I was getting. When I connected the computer back up I got something like in the second example pic. Consistent with that information the image disappeared overnight. I suppose parasitic capacitance could be one explanation.

If it happens again, I will try the screen with white as suggested. The article provides a nice easy way to do that.

The monitor worked OK for a couple of hours yesterday so if the problem occurs again, I guess the same treatment should work, i.e. let it 'rest' overnight. I'm still curious as to what causes the horrible flicker to arise in the first place, because whatever caused that, then led to the image retention problem arising.

« Last Edit: October 15, 2018, 02:15:22 pm by WaveyDipole »
 
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Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #13 on: October 24, 2018, 04:13:00 pm »
Well I contacted ViewSonic in the UK and was able to get the monitor serviced under warranty. Fortunately I was able to find a suitable box and sufficient packaging to box it up in. It was collected today and is en-route to the repairer. Will be interesting to see what they come back with.
 

Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #14 on: November 15, 2018, 02:43:26 pm »
Well almost three weeks had passed and I hadn't heard a thing, so I decided to send an e-mail to the repair company asking what the status of the repair was. Their reply informed me that the monitor was damaged on arrival "due to insufficient packaging"! Quite why it took three weeks and a prompt from me for them to acknowledge this I’m not quite sure, but they had already referred the matter to ViewSonic.

Now, I had expressed my concerns about shipping something so fragile beforehand and was given little advice other than being informed by the repair provider that they do not supply packaging. Previously when I had a laptop serviced under warranty, that particular repair provider had provided suitable and secure packaging. To be sure, I don’t expect such consideration for just any type of good, but given the rather precarious nature of sending an LCD monitor via a courrier, especially without the original packaging, I had perhaps hoped that some consideration might have been given to the safe shipping of such an item and that at least some advice would be given. Apparently this was my responsibility and my risk. Perhaps the approach depends on the repair provider involved.

For shipping, I was fortunate to still have a sturdy large box in which I had previously received a vintage oscilloscope from Holland (and that had survived intact), and an abundance of salvaged industrial quality bubble wrap type packing material. That stuff was probably about an inch thick, not like the rather thin stuff usually puchased at the stationary shop or post office. I also used a mixture of polystyrene blocks and small carboard boxes to fill voids, particularly for support behind the unit and multiple layers of padding over the screen. The box was also clearly maked “FRAGILE”. Unfortunately I didn’t have a larger box available to double-box the unit and had no means of obtaining one so I did the best I could with what I had available and in the knowledge that sending an LCD monitor was always going to be a risky proposition. Hoping for the best, I rather anxiously agreed to the collection.

In their reply, the servicing company had asked for a copy of the receipt again, so I e-mailed them back with another copy. In the subsequent reply I was informed that in general they do not cover second hand units unless the owner is able to provide the original purchase receipt from the original purchaser. Since the receipt I had provided initially was for my second hand purchase and it was a copy of this that I had just provided again, it is perhaps surprising that the warranty repair had actually been accepted when the case was logged. However, there was also some good news!

On this occasion, ViewSonic have, as a goodwill gesture, offered to send me directly, a  refurbished unit. I have been informed that this should arrive within the next 5-7 days. This has been gratefully acknowledged.

Assuming this arrives as anticipated, then I will have been very fortunate indeed! The lesson I draw from this is, that it is just far too risky to send an LCD monitor by courrier, no matter how well one thinks it might be packed, unless perhaps one has the original custom designed packaging. Otherwise this seems to be just asking for trouble. It is something I was rather anxious over in the first place and which I very much hesitated to do, and something that I not likely attempt again.
 

Offline Wan Huang Luo

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #15 on: November 15, 2018, 02:55:34 pm »
Dipole, its nice to see ViewSonic providing courteous customer service by sending you the refurb after all of the trouble you've been through.
 

Offline rdl

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #16 on: November 15, 2018, 04:50:35 pm »
Off topic, but I always try to save original packaging at least until the warranty runs out just in case. It's a good idea if you have the space. I guess I take it to extremes. I bought my first flat screen TV, a 37", in 2006. It broke in 2016. No doubt due to a power supply problem. A new TV was purchased right away to replace it, and it has been propped against the wall in my bedroom since then. I decided last week that it just wasn't worth fixing, but I still have the box it came in.
 
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Offline WaveyDipole

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Re: The viability of repairing modern LED backlit LCD monitors
« Reply #17 on: November 20, 2018, 12:48:18 pm »
Dipole, its nice to see ViewSonic providing courteous customer service by sending you the refurb after all of the trouble you've been through.

Yes, indeed it is. :clap: The replacement arrived today. Its the exact same model, looks like new and came complete with a power supply and HDMI cable. I'm using it now as I type this and have only been running it for a short while, but it seems to be working well. Strictly according to their policy ViewSonic didn't have to replace it but they did, so a big thumbs up to them.  :-+

BTW, regarding packing it came in the manufacturers original purpose made box which I will retain - just in case!
« Last Edit: November 20, 2018, 01:00:52 pm by WaveyDipole »
 


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