LG LCD TV BACKLIGHT BLINKING PROBLEM TROUBLESHOOTING - LG 60LB7100 INTERMITTENT BACKLIGHTS

LG LCD TV Backlight blinking problem troubleshooting - LG 60LB7100 Intermittent Backlights

Backlights Blink
• Backlights go OFF.

SMPS Trouble LED blinks 3 times then only 2 times.
Note: This panel was a Refurbished panel from parts.

Panel P/N: CRD31515701
TV ran for 4 days, 24 hours a day until symptom showed up.

The backlights would begin to blink. Usually 4 to 6 times then they would shut off completely.
• SMPS LED was blinking 2 times indicating DC-to-DC converter problem.
• However, when watching the SMPS trouble LED while the backlights were blinking, it blinked 3 times once or twice then it went to 2 times after the backlights went off. 3 times indicating Open LEDs.
• While Backlights were blinking: Reading the test points EL50-EL54 EL62-EL67 on the SMPS for backlight grounding signals, all but two test points were reading approximately 4V. But two of them were reading 0V, (EL55 and EL64). Backlight Power was 70V.
• While Backlights were off: Reading the test points EL50-EL54 EL62-EL67 on the SMPS for backlight grounding signals, all but two test points were reading approximately 7V.
But two of them were read 0V (EL55 d EL64). Backlight Power was 56V.
• Note: In this model there are only 6 backlight drivers. So two test points are tied together per/driver.

Reading the test points EL50-EL54 EL62-EL67 on the SMPS for backlight grounding signals, all but two test points were reading approximately 6V. But two of them were reading 0V, (EL55 and EL64).
Note: In this model there are only 6 backlight drivers. So two test points are tied together per/driver.
Example: EL62 and EL54 are tied together, EL55, EL64 are tied together, etc
Note: When the Backlights are “off”, the reading are 2V on good LED bars and “0V” on the defective bar.

LED (LD701) would blink 3 times while backlights were blinking and 2 times after the backlights turned off.

Note: LED (LD701) blinking 3 times indicates an open backlight LED feedback line.
Check the Test points EL50-EL54 EL62-EL67 for “20V” volts. This would indicate an Open LED driver.
Using a 100 ohm resistor, one end to ground, touch the other end to the Test Point pin that has “20V”. If the backlight comes on, the panel is good, SMPS is bad.

After disassembling the panel, we found that the connector to the bottom LED Bar was intermittent. The connector is attached by simply pressing it down onto the connector. The Red wire (B+) to the bar was intermittent making contact with the connections on the LED Bar. On all “A” bars, LED B+ arrives on the (-) marked pin on the connector. On all “B” bars, LED B+ arrives on the (+) marked pin.

This connector is inserted by laying it over the connector on the board and pressing down to press it into place.  For those unable to do panel disassembly, panel replacement is necessary.

The best repair method for this would be to remove the wires and solder them directly to the LED bar.

Avoid solder bridges. Cut the crimped connector off the wire first.
For permanent fix, you should do this to all “outside” connectors on the right and the left side of the LED Bars.
Note: You may need to un-tape the wire harness to allow for slack. Be sure to re-tape after repair.

Examine each LED to make sure they have not become un-bonded. “Do not life by the LED lens”. Over time, this could cause overheating.
if they have, press down on either side of the LED for about 60 seconds to rebond.  Do not press down on LED.