SONY LCD TVs-BACK-LIGHT INVERTER BOARD - HOW TO TROUBLESHOOT
SONY KLV26HG2 LCD PANEL ASSEMBLY
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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
