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Acer AL2416W 24" LCD monitor backlight half dark

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rustyx
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The backlight in my old Acer monitor is only half-lit and there comes a 50 Hz buzzing sound from the inverter transformers.
The LCD image itself is fine.

What could it be, the CCFLs, the inverter or the power supply, does anyone know? Are the CCFLs OK?

al2416w ccfl tubes

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yohnsee
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Hello,
does it run like this indefinitely? Or does the protection circuit shut down the lamps? CCFLs could be bad, but first check these:
The inverter board gets around 24V DC from the PSU. Does it drop significantly after the ignition of the lamps?
Also, after a few minutes turn the system off and check if the fets are extremly hot.

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rustyx
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It runs like this indefinitely, and there's exactly 24V on the bottom 5 wires going in to the inverter, and +2.3V / +2.7V on wires 2 / 3 from the top (why so many wires BTW?)

al2416w inverter wires

Couldn't check all the FETs as some are under a glued heatsink, but the 3 that I could reach were cold.
Also it sounds like the buzzing is coming from the bottom two transformers, or at least is more pronounced at the bottom half of the inverter.
And before it went bad, for a couple of days it was flickering for about a second on startup. Does that tell anything?

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yohnsee
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Well, it seem like the tubes are getting old, and can be ignited, but as you see, only partially holds up. There is one dangerous and one safe solution. The dangerous one is to locate the feedback loop from the high voltage transformers, and adjust the current to the tubes. However this is not recommended, as an accidentaly exploding tube can harm you. The safer solution is to order a LED kit from Ebay or aliexpress, and build it in. The voltages and dim inputs are ready available on the inverter board connector. Neither will be fast, nor profitable, but you can save a display from the garbage dump.

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rustyx
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Hmm, if a tube is bad, can one bad tube affect others like this? Is there a way to find which one it is? Is it safe to power on with some tubes disconnected?

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yohnsee
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As I see from the pictures, you have these "U" shaped lamps. So the right ends are the tips of the "U", they get the juice from those ends. These lamps are hard to find, I once tried to repair a LG 42" TV with such lamps, and there wasn't any reliable and cheap source to buy.
 

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rustyx
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The issue was two burnt FETs on the inverter board. The U-shaped lamps are all OK :-)

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yohnsee
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Hey, good to hear. Good job!

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