LG 50LB6100 Backlight on/off flicker

[jason123]

Hi folks.. got this TV that has the backlight unstable. On / off (just the backlight) - when on, you can see some intelligence on the screen. Frequency of on/off every few seconds

Disconnected the TCOn, and no luck ... still on/off backlight

Naturally I would start tear down to replace LED strips, but when I forced the power supply board to on (Shorting PR--ON and DRV-ON to 3.5V) I measured the left LED set (LED+ and LED-) and I get roughly between 54 and 64 V seems to fluctuate - not very stable. The other set of LED+ and LED- is reading 25 - 35V and occasionally spikes to 102 V or so.

I'm thinking this is possibly a power supply issue? I can order a new one or attempt repair, but curious to know what you guys think? I don't have any load on the LED Driver- Just a note
Thanks

[budm]

Re: LG 50LB6100 Backlight on/off flicker

You need to provide the LED Voltage readings of all 4 pins with ref. to chassis GND by keeping the black probe on the chassis, red probe one of the four pins then turn on the TV to see how high the Voltage jumps up to and then wait 5 ~10 seconds to see how low it goes down to and then turn off the TV, do the same on the other 3 pins. LED connector must be in place while you are doing this test.

[jason123]

Re: LG 50LB6100 Backlight on/off flicker

Ok, so the connector is labeled from right to left Pin1 = LED-, Pin 3 = LED+, Pin 5 = LED -, Pin 7 = LED+

Pin 1 as low as 8.xx V and as high as 14 V
Pin 3 as low as 88 and as high as 92 V
Pin 5 Stable at 0.175 V
Pin 7 as low as 194 V as high as 212 V

[budm]

Re: LG 50LB6100 Backlight on/off flicker

Ok, so the connector is labeled from right to left Pin1 = LED-, Pin 3 = LED+, Pin 5 = LED -, Pin 7 = LED+

Pin 1 as low as 8.xx V and as high as 14 V
Pin 3 as low as 88 and as high as 92 V
Pin 5 Stable at 0.175 V
Pin 7 as low as 194 V as high as 212 V

The LED string connected to pin 5 and 7 has open circuit.

[jason123]

Re: LG 50LB6100 Backlight on/off flicker

So teardown...i was hoping to avoid it. Can you elaborate how you determined this?
Thanks

[jason123]

Re: LG 50LB6100 Backlight on/off flicker

One LED was open as diagnosed - Thanks budm!! Set is up and running

[budm]

Re: LG 50LB6100 Backlight on/off flicker

Glad to hear, just make sure to turn down the backlights level as low as possible on all input modes.

[jason123]

Re: LG 50LB6100 Backlight on/off flicker

Done.. Thank you again for the help.

[jangammitesh@gmail.com]

Re: LG 50LB6100 Backlight on/off flicker

nice Co opreation