LG 47LG90 LED LCD TV - LED BACK-LIGHT TROUBLESHOOTING
BACK-LIGHT TROUBLESHOOTING
When dealing with the LED backlights that have a problem: Remember, two inverters control the LED backlights, so the screen is broken down into two sections. Then each inverter controls 8 sections of ½ the screen.
ENTIRE
PANEL WON’T LIGHT:
1) Is
the 24V being supplied to the Inverters from the SMPS? (CN1/CN501 Pins 1 ~ 5)
2)
Is the Inverter On Command arriving at both Inverters? (CN1/CN501 Pin 12) (Main
to SMPS P201 Pin 20)
3)
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:
1)
Confirm steps 1 and 2 above for the particular Inverter involved.
2)
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:
1)
Locating the connectors controlling that particular section should be easy, just
compare the section that is out and align with the particular cable.
2)
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;
3)
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.
4)
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:
1) Disconnect
the ribbon cables from the T-CON PWB to the Inverters, could be a T-CON
problem. (CN8/CN9).
INVERTER 'M' CONNECTOR [CN-1] VOLTAGES & RESISTANCES
- Diode Mode values taken with all Connectors Removed.
- BR1 (ADIM Pin 11) Fixed and not used
- 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.
INVERTERES 'M' & 'S' CONNECTORS [CN-304 & CN-804] VOLTAGE & RESISTANCE
- EXT_VBRBcan vary according to type of signal being processed, OSD Backlight setting.0.3V 0% to 3.4V 100% and the Intelligent Sensor. Output controlled from the BCM chip.
- Note: T-CON PWB Pin numbers are opposite.
- Diode Mode values taken with all Connectors Removed.
INVERTER 'S' CONNECTOR [CN501] VOLTAGE & RESISTANCE
- BR1 (ADIM Pin 21) Fixed and not used.
- Diode Mode values taken with all Connectors Removed.
INVERTER-S TROUBLESHOOTING [D302/D802 EXPLANATION]
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 of 1Hz. However, if there is an abnormality with the LED drives, they
will blink 5 times faster or 5 Hz.
TESTING THE BACK-LIGHT BLOCKS
