Jun 25, 2018, 12:40 AM
Post #2 of 3
Re: [mamomark] Sony KDL-46V25L1 standby light flashes 4x
[In reply to]
Backlight Protection (4X Flash Pattern)
Reference Figure 3-2
This protection mode monitors the operation of the Backlight Inverter Board and the Lamps. The Inverter Board is the Lamp power supply, which produces the high alternating voltage necessary to drive the Cold-Cathode Fluorescent Lamps (CCFL) used for the LCD panel backlighting. There are three main causes for the activation of this protection mode.
• Loss of 18.5V supply to the Inverter Board (at CN6202 on the G2-Board)
• Loss of 3.2V Backlight ON signal
• Defective Inverter Board Circuits
• Defective Lamp(s)
The following paragraphs are brief descriptions of each failure listed.
Loss of 18.5V supply to the Inverter Board (at CN6202 on the G2-Board)
The 18.5V is the power supply for the Backlight Inverter board. However, the 18.5V also drives two voltage regulators on the BU-Board (reference Figure 3-1). Therefore, if the 18.5V is lost due to a Main Power Supply failure a 5X flash pattern is generated. The Main Microprocessor generates a 4X flash pattern only if there is a loss of 18.5V at CN6203. In other words, the Main Power Supply is functioning OK (producing 18.5V), however, the 18.5V is not making it to CN6203. There is a poor connection or open circuit in the physical connection between the G1/G2-Board and the Inverter Board. Consequently, the Backlight Inverter fails to start, the Panel Detect line goes low (CN7009/pin 3), and the microprocessor detects a failure.
Loss of 3.2V Backlight ON signal
Confirm 3.2V at CN7009/pin 1 on the BU-Board.
The Main Microprocessor on the BU-Board turns on the Backlight Inverter using the 3.2V Backlight-ON signal. You can measure this voltage at CN7009/pin 1 on the BU-Board. If the Main Microprocessor fails to send this signal (rare occurrence) or if there is an open path (confirm secure & undamaged connectors between the BU-Board and the Inverter Board) to the Backlight Inverter board then the Panel Detect line goes low (CN8603/pin 4) and the microprocessor generates a 4X flash pattern.
Defective Inverter Board Circuits or Lamp Failure
Confirm 18.5V (Power Supply) and 3.2V (Backlight-ON).
In the case of an actual Backlight Inverter board circuit or Lamp failure, the 18.5V and the 3.2V voltages should be OK. Therefore, prior to shutdown you can measure these voltages to confirm that power supply and control signal are present. If these two voltages check OK, but the Backlight does not light and the Panel Detect line goes low (CN8603/pin 4) then the defect exists on the Backlight Inverter board or a Lamp(s) (Panel Assembly) has failed. Use the following procedure to determine whether the Backlight Inverter or the Panel Assembly is the defective component.
Caution: Do not attempt to directly measure the Backlight Inverter Board output directly. 1000V or greater is present at the outout on initail power ON.
The best way to check the Inverter Board output is to place your VOM probe on top of the individual plastic lamp connectors (reference Figure 2-2 & 2-3). Set the VOM to AC volts, place the probe on top of the connector directly above one of the two wires (each connector feeds two lamps). Place the VOM probe over each wire for proper measurements.
A good output will measure approximately 3VAC.
A bad output will measure aproxiamatey 1VAC or less.
If any single output is bad replace the Backlight Inverter Board.
If all Inverter Board outputs are bad, check the 18V supply voltage from the Main Power supply before replacing the Backlight Inverter Board.
If the 18V is missing check for loose or damaged connections between the G1/G2-Board and the Backlight Inverter Board.
If the 18V is present at the Inverter Board, however, all output are bad then replace the Backlight Inverter Board.
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