Tuesday, November 05, 2013

SONY LCD TVs-BACK-LIGHT INVERTER BOARD - HOW TO TROUBLESHOOT


SONY KLV26HG2 LCD PANEL ASSEMBLY
KLV-32M1 LCD PANEL ASSEMBLY
CLICK ON THE PICTURES TO MAGNIFY
The first thing to note when troubleshooting a possible defective Backlight Inverter is the AC current draw on the VAC (Variable AC Power Supply) at initial power up and ON states. The two states are as follows:
Initial Power Up 0.2A
After approximately 5 seconds the current will jump to 1.38A (Backlight ON, Standard Picture Mode, Backlight Adjustment MID range).
This is a quick indication if the Backlight Inverter is functioning. The AC current should jump to 1.38A to indicate a properly operating Backlight Inverter. NOTE: This does not indicate proper operation of the lamps themselves. The Inverter can be operating properly with a defective lamp.
Inverter Board Shut Down: (AC Current OK on initial power up, but unit shuts down).
If the unit is shutting down and going into protection mode after the AC current has momentarily jumped to 1.38A before shutting down, this indicates that the Inverter board is powering up, and something else is causing it to shut down. The most likely cause for the Inverter to shut down in this manner is:
One or more Back lights are defective.
Check the amplitude of the Inverter output waveform at each output connector. If the amplitude is excessively low as shown in waveform 2-3 the lamp is defective. Consequently, the complete Panel Assembly must be replaced. or lamps (or dark screen).
Inverter Board Not Powering Up: (AC Current Low on power up and unit shuts down).
If the AC current does not jump to 1.38A, and remains at 0.2A and shuts down, this indicates that the Inverter board is not powering up. Check the following voltages at CN8001 on the Inverter board.
16.5V supply voltage CN8001/pns 1 - 5
“Backlight” control signal CN8001/pin 12 (3.3V).
Inverter Board Detecting Defect:  (Video and Audio are momentarily seen and heard, but unit immediately shuts down).
The most likely cause of this symptom is a defective lamp or lamps, or an individual Inverter output drive is low or missing. The inverter is powering up and there are some lamps working because video is being displayed. This also indicates that the logic board is working (outputting video). The Inverter board is detecting a defective lamp, or individual inverter output drive. Make the following checks.
One or more Backlights are defective. Check the amplitude of the Inverter output waveform at each output connector as describe in the “Backlight Inverter Outputs and Inputs” section. If the amplitude is excessively low that individual lamp and/or the individual Inverter drive output is defective. Consequently, in either case the complete Panel Assembly must be replaced.
To confi rm the Inverter board is detecting a defective lamp check the “Panel Detect” line on CN8001/pin 11, which is typically 4V. This is an output signal from the Inverter board to the Main Microprocessor. This line will monetarily go to 4V and immediately go to 0V if a defect is detected.
Non-Functioning Inverter Board:  (Audio is momentarily heard, but No Video is displayed and the unit immediately shuts down).
In this case the most likely culprit is a non-functioning Inverter board (all outputs missing). Either the Inverter circuit itself is defective or there is a missing power source or control line. If the Inverter circuit is defective the complete Panel assembly must be replaced. Check the following to determine if the problem is in the Inverter or the supporting circuits.
16.5V supply voltage CN8001/pns 1 – 5
“Backlight” control voltage CN8001/pin 12 (this 3.3V voltage turns the Inverter circuit and consequently the Backlights).
If the 16.5V supply is missing, check for open connections or a defective primary power supply on the G1-board. If the ‘Backlight” control signal is missing, check for open connections and trace signal back to Main Microprocessor.  If both of these voltages are present and all Inverter outputs are missing, then the Inverter circuit is defective and the complete Panel Assembly must be replaced.
Defective LCD Panel:  (Missing Row(s) or Column(s) of Pixels)
Only a defective LCD panel can cause Missing Row(s) or Column(s) of Pixels. Since no supporting circuitry would cause this type of defect, when this symptom occurs the complete panel assembly must be replaced.
Check for the presents of the 16.5V supply on CN8001/pins 1-5. This voltage is developed by the primary power supply on the GL-board.
Check the following detect and control signals on CN8001 on the Inverter board.
Panel Detect – In normal operation 4V, which indicates a properly functioning Inverter circuit and lamps.   This is an output signal from the Inverter board that goes to 0V when it detects a failure in the Inverter circuit or in one or more lamps.
Backlight - 3.3V - This is an input signal to the Inverter board, which comes from the main microprocessor IC1006 on the B1-board to turn ON/OFF the Inverter circuit and illuminate the lamps.
Dimmer - 1V to 5Vdepending on the Picture Mode selected (Pro, Standard, or Vivid) This is an input signal to the Inverter board, which comes from the main microprocessor to control the luminance (or Dimmer) level of the Back-light.
KLV-26HG2 INVERTER BOARD
KLV-32M1 INVERTER BOARD