Monitor backlight turning off when signal cable plugged in

I have recently bought a faulty Samsung Syncmaster F2380 monitor in hope of fixing it and using it for personal purposes. The device used to work for a few seconds before turning off the backlight until pressing the power button. After opening up the device I noticed one cable of the CCFL backlight had burnt at the solder point on the CCFL tube. After resoldering the connections to the tubes and checking everything else I reassembled the whole thing back together.

Unfortunately now the monitor turns its backlights off when plugging in a signal cable (e.g. VGA or DVI), but remains on when not plugging one in (except it outputs the expected "Check signal cable" because nothing is plugged it)

I have also checked all capacitors on the main power board, as the CCFL lamps connect directly to it. I do not know how to check whether the CCFL Lamps are working or where the issue lies, but its just strange that the backlights only turn off when plugging in a signal cable. I would get an image for a few seconds, then the backlights would turn off. Perhaps the device turns on additional backlight lamps when it receives a signal?

I will open it up again sometime, and check which lamps actually turn on or not when plugging in a signal cable.

I really dont know what things to check next, so I would really appreciate help on this topic (especially as many others are having this issue as well)

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It seems to me that something is overloading, and that the backlight turning off is a symptom of a greater problem, faulty or burnt out capacitors somewhere perhaps.

I can see that there are two dvis and vga port on it, does this happen when a cable is plugged into ANY port? Does the BL turn off when a cable is plugged in to the monitor but not a device on the other end?


I might try replacing most caps on the power board anyways for now.

The backlights dont turn off because of a short circuit when a cable is plugged in. Rather they only turn off when there is a video signal coming in from any of the ports. Only plugging in any video cable doesnt make them turn off.

I noticed that the device outputs the "Check signal cable" message with one set of backlight tubes unplugged, while with the other set unplugged the transformer makes a weird noise and doesnt output anything at all.

Actually, every time the CCFL lamps turn on the first time or when they go off the power boards transformer makes a little high pitched noise. With no video cable plugged in and while it is waiting for signal the backlights are on, and the transformer does not make this sound. Sadly I cannot find a replacement transformer anywhere though.





I believe I have figured it out.

Upon inspecting the components even closer again after Conor Bailey above suggested to check for burned caps or similar, I noticed a slight yellow taint to the text ontop of the backlight inverter (as seen on the images below). After desoldering the transformer spool and flipping it around, I could immediately see a part of the spool being covered with black material and that it was a bit burnt.

It appears as if the inverter spool somehow got overloaded and burnt its wires at one winding. As the transformer is directly connected to the backlight ports (by tracing the pcb from the transformer), this explains why they turn off as soon as more load is running through (exactly what happens when a signal cable is plugged in -> the backlights need more power and additional backlights get turned on)

If you have this or a similar issue, make sure to check the backlight inverter transformer, as they commonly get a burnout on their bottom side!

Block Image

Notice how the windings of the spool look clean on the lower part of the picture, while one winding segment (where my tweezers point to) at the top part of the picture is completely burnt. Checking the resistances confirms that indeed electricity can't get through that part of the spool. The extreme heat the transformer gives off while running also confirms the above, as there is much greater resistance.

Block Image

The next step is to find a fitting replacement part, oh well!


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