LG 42LB5600-UZ No Backlights, All Test Good

[philtvman]

Getting no backlights with this one. Checked LED+ to chassis when plugging the TV in and the voltage spikes to 260ish then drops down to around 100 signaling to me it has an open LED circuit. Opened it all up, but all the LEDs turned on just fine.

Any suggestions where to go from here?

Edit: Guessing one of the LED cables wasn't secured all the way into the connector. Pushed it in when testing the LED voltages and now it seems to be working fine now.

[CapLeaker]

Re: LG 42LB5600-UZ No Backlights, All Test Good

yeah, just wanted to say to check the cables and connectors.

[philtvman]

Re: LG 42LB5600-UZ No Backlights, All Test Good

yeah, just wanted to say to check the cables and connectors.

Spoke too soon. Tested fine for about 15 minutes, then backlights all turned off.

[Andrew F. Ali]

Re: LG 42LB5600-UZ No Backlights, All Test Good

Bridge the interconnectors (if that applies) or just solder the wires in place.

[philtvman]

Re: LG 42LB5600-UZ No Backlights, All Test Good

Bridge the interconnectors (if that applies) or just solder the wires in place.

Double checked all LEDs with a tester, all checked out fine. I hooked it all back and up and set the backlight brightness to zero. The set worked fine for a couple hours, then the backlights turned off. LED voltage was around 84 after they shut off.

Ideas?

[budm]

Re: LG 42LB5600-UZ No Backlights, All Test Good

84V is the feeding Voltage to the LED driver boost converter circuit, so if you leave the black probe on the chassis and Red probe on the LED+ and then turn on the TV you will probably see the Voltage jumps up over 200V, sounds like you have open circuit some where in the LED string or bad LED's to me.
Tester only puts out 30mA so it is not 1005 real test as compare to real LED drive current of 300 ~ 400 mA range and that is when bad connection (bad contact resistance), or bad LED will show the symptom.