Hi all,
I've got an LG Flatron 24EN33TA with a backlight issue. The problem began with the monitor not powering up after sitting for a long time (overnight or during the day throughout work). When I would wake the computer up, the backlight would flick on for a second then go out. Sometimes it would take many tries to get it to come on. Once the monitor came on, it worked flawlessly until another long duration of being powered off.
I thought the problem would be bad caps but I checked both of the caps on the board and they are fine. I also tried powering the monitor from the bench power supply to rule out the DC power adapter.
When the backlight fails to stay on, the LCD panel itself is still displaying the image. If the monitor is left "on" but with the backlight still off for several minutes, the backlight will light and stay on the very first try. It's like something is warming up and allowing the backlight to work after it has been powered up for a while.
To test this theory, I used a thermal camera to see which components warm up when the backlight is in the failed state. The only noticable heat sources are the main processor and the 8 pin chip right by the display ribbon cable. I then froze the chip and the processor with some freeze spray to see if I could get the fault to return. I cannot get conclusive results on where the problem is. If I thouroughly freeze the entire board, I can get the backlight to fail, and warming the board with a hot air gun makes it work again. However, freezing just the processor or other components individually is hit or miss.
As a test, I tacked a low value, high wattage resistor over top of the main processor and connected it to the DC input (as shown in the photo). The resistor heats up to ~80-90°C. With the "preheater" resistor in place, the monitor still does not start by itself, but will start up first try 95% of the time if power cycled immediately after waking the computer. So it clearly has made a dramatic improvement.
I am assuming that the display's firmware is stored on the Winbond memory chip on the board so I should be able to buy new processor IC and replace it without having to worry about programming? The processor is a Novatek NT68655UFG, but there is no information available for it.
Has anyone seen this type of fault before or have any other suggestions for things to check?
Worst case I can come up with a small board to output the PWM signal to run the switching MOSFET for the backlight circuit and just have it run independently of the processor. However, I would like to fix it properly if possible.
I've got an LG Flatron 24EN33TA with a backlight issue. The problem began with the monitor not powering up after sitting for a long time (overnight or during the day throughout work). When I would wake the computer up, the backlight would flick on for a second then go out. Sometimes it would take many tries to get it to come on. Once the monitor came on, it worked flawlessly until another long duration of being powered off.
I thought the problem would be bad caps but I checked both of the caps on the board and they are fine. I also tried powering the monitor from the bench power supply to rule out the DC power adapter.
When the backlight fails to stay on, the LCD panel itself is still displaying the image. If the monitor is left "on" but with the backlight still off for several minutes, the backlight will light and stay on the very first try. It's like something is warming up and allowing the backlight to work after it has been powered up for a while.
To test this theory, I used a thermal camera to see which components warm up when the backlight is in the failed state. The only noticable heat sources are the main processor and the 8 pin chip right by the display ribbon cable. I then froze the chip and the processor with some freeze spray to see if I could get the fault to return. I cannot get conclusive results on where the problem is. If I thouroughly freeze the entire board, I can get the backlight to fail, and warming the board with a hot air gun makes it work again. However, freezing just the processor or other components individually is hit or miss.
As a test, I tacked a low value, high wattage resistor over top of the main processor and connected it to the DC input (as shown in the photo). The resistor heats up to ~80-90°C. With the "preheater" resistor in place, the monitor still does not start by itself, but will start up first try 95% of the time if power cycled immediately after waking the computer. So it clearly has made a dramatic improvement.
I am assuming that the display's firmware is stored on the Winbond memory chip on the board so I should be able to buy new processor IC and replace it without having to worry about programming? The processor is a Novatek NT68655UFG, but there is no information available for it.
Has anyone seen this type of fault before or have any other suggestions for things to check?
Worst case I can come up with a small board to output the PWM signal to run the switching MOSFET for the backlight circuit and just have it run independently of the processor. However, I would like to fix it properly if possible.
Attached Files
But today, I’m making an exception here. Why? No idea. Perhaps only because the repair details are still “fresh” in my head… which is ironic, given this is a 16 year old monitor that hardly anyone will care about today. It is new to me, though. 
I picked it up last November from someone on my local Craigslist. It wasn’t very close to where I live, but was close to a family friend that I had to go visit anyways. So after watching the posting on Craigslist for a few weeks and seeing it getting...
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