LG 55LB6100 Led blinks every 4 seconds

[henryvrensburg]

Good day guys

I got the above-mentioned TV from a friend with the following symptoms. Upon switch on, the LG logo will flash momentarily with intervals off around four seconds. I thought it was a backlight issue and ordered a brand new set from SJ. The new set arrived and I installed it with care, making sure it is installed as it should.

When I switched the TV on afterwards, it came on, everything working, but the backlights would slightly blink every 4 seconds. I bought a backlight tester, testing the backlights within the set. With the TV switched on, and driving the backlights with my backlight tester the blink still occurs. I asked the wonderful guys at SJ for advise and they send me a new set of backlights again, and I installed them. Before I put the chassis back I tested the backlights, all working with the following solid voltages(reading on my backlight tester)
LED bank 1 = 186V
LED bank 2 = 124V

After I re-assembled the TV, I switched it on it came on with the same 4 second blinking. I took the following readings of the connector

On connector without LED's (with negative on chassis)
Bank 1 = Range between 226V and 197V
Bank 2 = Range between 173V and 160V

On connector with LED's(negative on chassis)
Bank 1 = 241,1V solid
Bank 2 = 161V solid

On connector with negative on LED-
Bank 1 = Solid 172.8V
Bank 2 = Solid 113.7V
No fluctuations

I've read all the previous threads on this issue, it just seems unlikely that two brand new sets of backlights will have the same issue.

Thank you guys for any ideas

[nomoresonys]

Re: LG 55LB6100 Led blinks every 4 seconds

Are the backlight connections good and solid, not loose at all?

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Hi nomoresonys

I checked the connections. They are connected well, no bad connections

[budm]

Re: LG 55LB6100 Led blinks every 4 seconds

Lots of stuff do not make sense to me:
1) With the TV switched on, and driving the backlights with my backlight tester the blink still occurs. How do you drive the two strings of the LED st the same time with the tester? For it to blink the curent or the Voltage applied to the LED cannot be steady.
2) On connector with negative on LED-
Bank 1 = Solid 172.8V
Bank 2 = Solid 113.7V
No fluctuations
The two LED - are the rectum lines for each LED strip, so to have that much Voltage on the LED - do not make any sense. With that much Voltage on the return line, it means you will have very little Voltage for the LED strings.
3) If you look at the LED Voltage chart for 55" TV, one of the LED power supply is rated at 218v @ 230mA with load for the large LED string, for the smaller second LED string, the power supply is rated at 205V @160mA with load. Your report shows as: On connector with LED's(negative on chassis)
Bank 1 = 241,1V solid: This is not right.
Bank 2 = 161V solid: this is not right.

On connector without LED's (with negative on chassis)
Bank 1 = Range between 226V and 197V: It should be a lot higher without LED connected.
Bank 2 = Range between 173V and 160V: It should be a lot higher without LED connected.

https://assets.shopjimmy.com/media/c...072101-top.jpg

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Hi Budm

You are right, I could only drive one set of Backlight banks

The readings I got from the backlights were with the negative probe on LED- and the positive probe on LED+. You think this is incorrect.

Looks as if you think it might be the Power Supply board because of low voltages to the Back Light Strip

[budm]

Re: LG 55LB6100 Led blinks every 4 seconds

On connector without LED's (with negative on chassis)
Bank 1 = Range between 226V and 197V
Bank 2 = Range between 173V and 160V

On connector with LED's(negative on chassis)
Bank 1 = 241,1V solid
Bank 2 = 161V solid

On connector with negative on LED-
Bank 1 = Solid 172.8V
Bank 2 = Solid 113.7V
No fluctuations

But I thought all your readings are ref. to chassis.

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Only the last reading is with Positive probe on LED+ and Negative probe on LED -. After I read your first answer, I realized it's probably not a reading one should take. All other readings are Negative Probe on Chassis, except on the Main CAP where it is on the ground of the CAP

[Tvbob]

Re: LG 55LB6100 Led blinks every 4 seconds

Sounds like the power supply can't supply enough current to drive the led's...
Try turning them down in the menu.

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Hi tvbob, I've tried to turn the backlights down in the Menu, but with no success.

[neilc6]

Re: LG 55LB6100 Led blinks every 4 seconds

I just repaired this model. Symptoms were backlights flashing and found four shorted LEDs and one strip had an open. If the backlights are flashing, you have a bad LED somewhere or a bad connection to the strings.

The backlights will come and the tv will turn on with the LCD panel disconnected. I usually check before and after I put the diffuser back on.

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Hi Neilc6

I replaced the backlights twice with brand new sets from SJ. I checked the connections, and I couldn't see any bad connections. The TV just slightly blinks every 4 seconds or so. It's more of a slight dim than anything else.

[neilc6]

Re: LG 55LB6100 Led blinks every 4 seconds

Can you provide a picture of the backlights lit up with the panel and diffuser removed?

[nomoresonys]

Re: LG 55LB6100 Led blinks every 4 seconds

.

[nomoresonys]

Re: LG 55LB6100 Led blinks every 4 seconds

Maybe similar issue here? https://www.youtube.com/watch?v=WNZCMgsQMAM

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

Sorry guys, have been away for a few days.

This is my second pair of brand new set of backlights. Bought from SJ.

I'm reluctant to strip down to the backlights again, but will do so. Will keep you posted

[henryvrensburg]

Re: LG 55LB6100 Led blinks every 4 seconds

HI guys

I decided to strip the TV down to the backlights. The attached photo is off the backlights. I can see no problem with them. They are all burning exactly the same, they are the same brightness, I also cannot discern any bad connections. I replaced the panel, testing at every stage, I could only see the slight dim again when the panel was connected to the T-CON board.

Is it possible that the backlights fail only on brighter settings, although I turned them down in the MENU to aroaund 40%.

Can it be the panel?

[nomoresonys]

Re: LG 55LB6100 Led blinks every 4 seconds

Test the little capacitors on tcon board for shorts, diode mode, meter probe on each end, might beep if there's short somewhere on tcon or driver board.