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Inleiding

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.

  2. 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.

  3. 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)

Conclusie

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

6 andere personen hebben deze handleiding voltooid.

Thomas Widmaier

Lid sinds: 05-03-13

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Caution!

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

Walter Holzwarth - Antwoord

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 - Antwoord

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 - Antwoord

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 - Antwoord

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 - Antwoord

I ordered a a new transformer TM-09176 (T301) from ebay for less than 10 EUR and replaced the existing one and now the monitor works again without any issues! ~ thanks your your tip!

When checking the circuit with the thermal imaging camera after replacement, i can confirm that the transformer and also the resistor R301 beside it, do NOT HEAT UP any more. (the temp of R301 stays below 32°C which is fine). Measuring the temperature of the transformer and resistor seem to be a good indicator if things are broken.

@goaty I could send you the thermal-image if you like to add it to your description. Beside the board no BN44-00238 you may also add the transformer no “TM-09176” to your introduction as well - as this is the main part that needs to be replaced.

Dumbo - Antwoord

@Dumbo Great it worked. I added the transformer model number. Can you add the thermal image yourself or upload it someewhere, because I cannot post an email here.

Thomas Widmaier - Antwoord

Due to lack of diagnostic tools and skills I tried this fix blindly, purely based on having the same symptoms (backlight turns off after a second). Being inexperienced with soldering, the component swap was kind of annoying, but well within doable realms. Only fairly big soldering points need to be worked on. The monitor still turns on, so I think the swap went alright, but unfortunately for me the problem persists. Seems my monitor is destined for the graveyard after all :( so be it known, same symptoms can appear for different reasons.

MisterD - Antwoord

What is the resistance of R301? I am getting open circuit for that. The colour coding is misleading as I am not sure which way to read the colour coding

Andrew Chan - Antwoord

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