LG 47LG90 LED LCD TV - BACK LIGHT INVERTER "S" - TROUBLEHOOTING - CONNECTOR VOLTAGE CHARTS
When dealing with the LED backlights thathave a problem: Remember, the LED backlights are controlled by two inverters, so the screen is broken down into two sections. Then each inverter controls 8 sections of ½ the screen.
ENTIRE PANEL WON’T LIGHT:
- Is the 24V being supplied to the Inverters from the SMPS? (CN1/CN501 Pins 1 ~ 5)
- Is the Inverter On Command arriving at both Inverters? (CN1/CN501 Pin 12) (Main to SMPS P201 Pin 20)
- Disconnect the ribbon cables from the T-CON PWB to the Inverters, if backlights turn on, could be a T-CON problem.
½ THE PANEL WON’T LIGHT:
- Confirm steps 1 and 2 above for the particular Inverter involved.
- Disconnect the ribbon cable from the T-CON PWB going to the particular Inverter involved, could be a T-CON problem. (CN8/CN9).
SECTIONS OF ½ THE PANEL WON’T LIGHT:
- Locating the connectors controlling that particular section should be easy, just compare the section that is out and align with the particular cable.
- Looking at the connector going to the LED backlights, look at the bottom 2 pins on the M inverter or the top 2 pins of the S inverter, check for 39V? If missing, unplug the connector and recheck. If still missing, continue;
- Using the Interconnect diagram, locate the fuse protecting the 24V to the DC to DC converter that’s developing the 39V for that connector, if open replace the inverter.
- Be sure to test the Backlight LEDs that attach to that connector for shorted condition. With the connector unplugged, put the Red lead on the bottom 2 pins on the M inverter or the top 2 pins of the S inverter and the Black lead on any other 8 pins. All should read open. Or apply 30~38V on the bottom 2 pins on the M inverter or the top 2 pins of the S inverter and the (-) lead to any of the other 8 pins while observing that section of the panel, the LEDs should illuminate across the screen in the section controlled by that plug.
ENTIRE PANEL BACKLIGHTS ARE DIM:
- Disconnect the ribbon cables from the T-CON PWB to the Inverters, could be a T-CON problem. (CN8/CN9).
- D302 and D802 are LED visual indicators about the condition of the Inverters. If the inverters and backlight LEDs are running normal, these LEDs will be blinking at a rate of1Hz. However, if there is an abnormality with the LED drives, they will blink 5 times faster or 5 Hz.
CHECKING CRYSTALS
INVERTER 'M' CONNECTOR 'CN-1' VOLTAGE AND RESISTANCE CHART
- Diode Mode values taken with all Connectors Removed.
- Ext_VBRA (PDIM Pin 13) can vary according to type of signal being processed, OSD Backlight setting. 0.9V 0% to 3.4V 100% and the Intelligent Sensor. Output from the BCM chip.
INVERTER 'S' CONNECTOR [CN-501] VOLTAGE & RESISTANCE
