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Introduction

The backlight of the display does light up only for a few seconds, one reason is a defective transformer in the inverter stage of the power supply.

In this case, a few windings of the transformer have an short circuit, causing the resistance of the two secondary coils to be different.

The fault of transformer can be detected by measuring the temperature of the transformer left and right side using infrared thermometer or thermal imager. The temperature will differ greatly.

Power supply model number is BN44-00238

  1. Remove power cord. Remove the display stand by removing the two screws on the round plate on the backside of the monitor Open up the backside of the display (display placed face down on cloth to avoid scratches) by carefully releasing the snapped in latches using a screwdriver or opener tool.
    • Remove power cord.

    • Remove the display stand by removing the two screws on the round plate on the backside of the monitor

    • Open up the backside of the display (display placed face down on cloth to avoid scratches) by carefully releasing the snapped in latches using a screwdriver or opener tool.

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  3. The metal cage housing the PCBs as just stuck to the backside of the LCD. Carefully remove adhesive strips, release the cables to LCD and front panel buttons.
    • The metal cage housing the PCBs as just stuck to the backside of the LCD.

    • Carefully remove adhesive strips, release the cables to LCD and front panel buttons.

    • Remove SMPS PCB (switching mode power supply) by removing screws around.

  4. Caution: Touching the capacitor wires may cause serious injury. Use a capacitor discharge probe to safely rid the capacitors of dangerous charges. From power board desolder transformer. It has 6 pins on one and 4 pins on the other side. Replace with new transformer. (Model TM-09176)
    • Caution: Touching the capacitor wires may cause serious injury. Use a capacitor discharge probe to safely rid the capacitors of dangerous charges.

    • From power board desolder transformer. It has 6 pins on one and 4 pins on the other side.

    • Replace with new transformer. (Model TM-09176)

Conclusion

To reassemble your device, follow these instructions in reverse order.

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Thomas Widmaier

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7 Comments

Caution!

Myrra 12 V AC Transfor 5VA is not compatible with TM09176

Walter Holzwarth - Reply

Hi, I have the same issue with the same monitor. But in my case, the transformer has equal temperature on both sides. Is there any way for me to check if it’s really the transformer or something else?

One more thing, there is a high-pitched noise coming from the upper part of the screen (probably the backlight), after the screen goes dark again. Thanks!

Kristijan Žganec - Reply

High pitched noise is probably the resonance of a coil either the transformer or another inductor of the swtiching regulator circuit.

You could try and measure the inductance / resistance of the transformer (desolder first) and check if they match very closely.

Thomas Widmaier - Reply

I took some thermal images (using SeekTermal camera) from the power-supply board of this TV:

The rectangular black transformer TM-09176 (T301) gets 60°C at one side only. But the resistor R301 beside the transformer, gets nearly 100°C! This is maybe due to unregulated high current coming from the transformer? The rest of the board stays very cool.

Dumbo - Reply

Measure if there is any short circuit to ground with resistance or continuity mode around the resistor that gets hot.

Maby the CCFL Tube or wire is shorted ?

Thomas Widmaier - Reply

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