Backlight replacement of the LG Flatron 194WS monitor.

This all started when the backlight would only stay lit for about one second. At first I thought it might be due to a power supply issue. There is previous history on this subject, because there are a few monitors built around the same internal hardware. I followed the instructions there (thank you Corporate Computer) and replaced those six capacitors.

I still had a faulty backlight. For reference, the power board has the following part number EAX35159301/7, and is auto-ranging in its input supply (100-240VAC, 50/60Hz). It has a revision date of 2007-02-26.

So the next thing is the CCFL backlight tubes, so I stripped those out from the panel assembly. The ends showed significant blackening, so perhaps the power supply was responding to an over-current condition on the CCFL by shutting down. Sadly, ebay and google could not find me a cost-effective set of replacement tubes. Also, some six years after the unit was made, LED backlighting has made CCFL backlighting obsolete.

While I had the panel apart, I cut some notches out of the metal surround.

So I went back to ebay and bought one metre of white SMD LED flexible tape. It cost me £1.49, and that included postage to the UK.

The tape was designed so it could be cut every three LEDs, and there are cut marks on the tape. It worked out that I could cut two lengths, each with 24 LEDs. These would fit the top and bottom of the screen, where the CCFL tubes used to be. The tape was 8mm wide, exactly the same as the metal supports for the CCFL tubes. The LED strips require 12VDC, which I could get from the monitor’s own (internal) power supply. If you look where the smaller LCD controller board connects to the power supply, via an 11-way connector, the connections there are clearly labelled.

Having used the adhesive backing on the LED strips to secure them to the metal supports, and lots of compressed air to clean the various light diffuser sheets, reassembly was straight-forward. It was mostly straight-forward. After connecting the LED strips to the power supply, I did a final test before assembling the outer casing.

Summary.

The result is that the monitor now works, although the backlight is noticeably dimmer than it used to be before it failed. Also, the backlight stays on when the monitor is in stand-by mode. The only way to turn off the backlight is to isolate the monitor at the mains inlet. Given the very small amount of money spent on it, I think these are acceptable compromises.
Something to consider doing is going back to that 11-way connector, and looking if there is a control signal which can be used to drive a simple MOSFET switch, so that the backlight is extinguished when there is no input signal, or when the monitor is in stand-by.

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4 Responses to “Backlight replacement of the LG Flatron 194WS monitor.”

  1. Stoatwblr Says:

    I’ve just done the same thng, using a LED controller, rather than feeding directly off 12V. This has “enable” and “dim” controls. It adds about $8 to the total price but I think it’s worthwhile as it will protect the rest of the circuitry in an overcurrent condition (and it actually switches the leds off!)

    BTW, you don’t need to dismantle the entire panel to pull the CCFLs. Just unscrew the (tiny) CCFL lamp channel retainiing screws (opposite end to the wires), remove the front metal bezel, unclip the wires and pull gently on them. The entire channel assembly will slide out.

    Reassembly is the reverse but make sure you fit the wires back into their plastic guides before refitting the front bezel.

    • Stoatwblr Says:

      It’s a good idea to remove the existing CCFL transformer from the board when you convert to LED. This will ensure the inverter is completely shut down and safe – plus it leaves a spot to mount the led controller.

  2. barrowbiker Says:

    I found out later that you can buy ready-made LED strips, with controllers, which have more LEDs per unit length for brightness etc. At the time I needed to fix the monitor quickly.
    Thanks for the tip about removing the transformer.
    After disassembling the entire panel, I realised I didn’t need to just to get the CCFL lamps out.

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