LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

[philtvman]

Had the issue where the screen flashes for a second when plugged in, but turns off instantly. It won't do it again until the power is dispersed from the boards (unplugging and holding power button down). Figured it was likely just a bad LED somewhere based on the symptoms and other threads I found here. When watching it flash, it was clear there were a couple strips not coming on at all.

I cracked it open to check the LEDs and every one of them turned on with the tester (which was pretty annoying to be honest). I plugged the set in with the dispersion panels off to see exactly which LED strips were not turning on (pic attached). I took the picture, unplugged the TV, pressed power button, plugged TV back in, and everything turned on normal. Figured maybe it was a loose connection that got secured. Let it run for about 30 minutes and all worked great. I started to put it back together, testing it every step so I wouldn't get too far and realize it was still messed up. Eventually, it began the same symptoms.

The 4 strips that don't turn on are all tied to the LED 1 lead. When plugged in, voltage jumps to 80V, panel flashes, and it settles back down to around 60V.

I know that the LED tester doesn't put out the same load as the power board so sometimes it can be misleading. Would it just make sense to go ahead and replace the 4 LED strips or is there another way to test their 'health'?

[neilc6]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

There is probably an intermittent LED in those strips. I would just replace them. I have seen LEDs that have a delayed turn on with a tester which I typically will replace as well.

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

You have six set of LED strings, LED 1 ~ 6.
The six LED + 1 ~ 6, each is the Anode pin of each LED string and they are all tied together and fed by the 80V power supply, the six LED - 1 ~ 6, each one the Cathode return for each LED string.
What you can do is to swap the strips with the working strips to see if the problem will follow or not.
You also have surface mounted connectors on the LED strips which are known for bad solder joints so you may want to inspect that.
The LED tester may give a clue about the bad LED, you have to look at the Voltage reading on the tester and see if any one of the six LED string is unstable not and if the Voltage is much different than the other string, it is not 100% but it may give enough clue.
It is big panel so you should replace all the strips at the same time, try swapping them first.
Parts for yiur TV: https://www.shopjimmy.com/catalogsea...?q=LG+65UH5500

[philtvman]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

Brilliant suggestion swapping the strips, feel like an idiot for not thinking of that. Was able to track down the specific strip causing the problems.

Thanks so much for the quick help

[budm]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

What does the LED tester show when test that bad strip?

[anthonystv]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

Ground the Fail pin and turn the tv on it will stay on

[steviewonder]

Re: LG 65UH5500 Momentary Flash Of BackLights (Occasionally)

Another common problem is intermittent arcing of the rather crappy plug jumper that connects one strip to the adjacent strip...have a close study there,that is most likely problem. Seen this lots of times. Simply jumper over the top of each one.