LG TV purple patches.  - Page 1
Forum section: electronics / repair

author: Sounduser
author_rank: Contributor
timestamp: February 28, 2021, 12:23:45 pm
content: Hi boys and girls.My led TV back light... There are a few LEDs turning purple. This seems to be a quite common problem to have back light LEDs turning purple. Mine isn't that back yet.Looking online you can get a set of replacement LED PCBs for about 50 quid.But I was wondering if anyone knows about the LEDs themselves? Are they anything special?Or could I order some high cri neutral LEDs with the same package and just hot air / hot plate swap all the LEDs???From the picture it just looks like a long aluminium backed PCB.Thanks guys.

author: wraper
author_rank: Unknown
timestamp: February 28, 2021, 12:30:18 pm
content: The issue with replacing single LEDs is that they will not match in brightness and color tone with the rest unless you are very lucky. Also if a few LEDs became bad, the rest are on their way to fail as well. If you want to replace LEDs, not strips, the correct way is to replace them all, which is a lot of work.

author: Sounduser
author_rank: Contributor
timestamp: February 28, 2021, 12:33:51 pm
content: Yeah. I would replace them all at once.

author: wraper
author_rank: Unknown
timestamp: February 28, 2021, 12:58:45 pm
content: You need to be aware that even if LED has the same package, it may have different polarity. Also in older TV usually single die was used within LED but later 2 dies in series in the same package became common and with double of forward voltage. For example LG had led strips which looked the same but newer had 2x Vf. So you should ensure you are buying the right thing.

author: Sounduser
author_rank: Contributor
timestamp: February 28, 2021, 01:52:09 pm
content: Just read someone posted online that the lenses are very hard to realine. Which left the picture patchy. Might just have to buy the replacement parts.

author: wraper
author_rank: Unknown
timestamp: February 28, 2021, 02:01:48 pm
content: Where did you get 50 quid figure BTW and what tv/lcd model is it? You probably can get them a few times cheaper from Aliexpress with fast shipping from UK warehouse.

author: Sounduser
author_rank: Contributor
timestamp: February 28, 2021, 02:13:00 pm
content: It's an of 43" 4k TV.AliExpress has them for 15They're on eBay for around 50And there is some so-called genuine LG ones for 80As it's not really bothering me at the moment. I might try the AliExpress ones. In no rush and not have anything to lose.Thanks.

author: TheMG
author_rank: Frequent Contributor
timestamp: February 28, 2021, 04:32:57 pm
content: I would go with the genuine replacements.Reason is, if the replacement LEDs don't have precisely the same CRI and color temperature as the originals, the colors will come out incorrectly.Fact is, no white LED is perfect over the whole spectrum, and the manufacturer will have to some extent calibrated the TV to compensate for that.Word of advice, once you've replaced the LEDs, turn that brightness setting down! On some TVs the LEDs run way too close to maximum ratings at high brightness levels. If you keep the brightness setting below 80%, preferably even lower, you will extend the life of the LEDs dramatically.

author: wraper
author_rank: Unknown
timestamp: February 28, 2021, 05:01:07 pm
content: Quote from: TheMG on February 28, 2021, 04:32:57 pmThe fix is to increase resistance of current sense resistor in LED driver to decrease max current by about 25-30%. Brightness decrease is not very noticeable.QuoteChinese LED strips are OK. Not that these TVs are decently calibrated to begin with or LED original strips will necessarily come with exactly the same LEDs. Nor I would count those genuine LED strips are actually genuine since LG supplies whole LCD panels to their service centers, not LED strips. As of 50 quid strips, most likely they are the same cheap LED strips from Ali sold at huge markup.

author: Sounduser
author_rank: Contributor
timestamp: February 28, 2021, 09:41:45 pm
content: The LEDs that were originally fitted can't be great. They're seems to be loads of Samsung and lg the with blue / purple spots or total screens.

author: TheMG
author_rank: Frequent Contributor
timestamp: February 28, 2021, 10:05:04 pm
content: Driven hard and run hot, the phosphors degrade resulting in the light output becoming more and more blue (white LEDs are actually blue LEDs with a phosphor coating to produce white light.Maximum brightness for minimum $$$. Thin and light TVs with minimal heatsinking for the LEDs. Also the default brightness setting is often at 100%, to give buyers that "wow" factor, and make the TVs stand out on store displays too.So not necessarily poor quality LEDs, but rather some design choices that don't really favor long term reliability. It's all a numbers game these days to sell as many TVs as possible and at the highest profit margin, and they really don't care about making a long-lasting product as long as most of the units make it through the warranty period. Especially these days with "smart" TVs people are upgrading them just for the new features (yay planned obsolescence!!!).

author: amyk
author_rank: Super Contributor
timestamp: February 28, 2021, 10:12:09 pm
content: That sounds like phosphor degradation. White LEDs are just blue LEDs with a yellow phosphor coating to make them emit white light. If the phosphor is dead or dying you get bluish-purple instead.