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is this an inverter or backlight issue?

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New Member
Hey All,

Need expert help. I brought out my old HP 2509M monitor to the light from my closet and decided to fix it. After resoldering a couple of mosfets and diode, the power button became functional. Upon switching on I immediately noticed that the backlight didn't turn on, so the screen was black. I hooked up the monitor to my PC and put a flashlight to the screen. I could see my duplicate desktop which was very dim. Now from what I understood, having gotten to this point this still could be an inverter or backlight issue? Right? Correct me if I'm wrong here. I proceeded to take apart the monitor and got to the backlights. One pair was charred and crispy, the other seemed to be okay. I have no idea what a dead backlight looks like physically. No char or burn marks on this pair unlike the other. I then reassembled the monitor without the backlights and hooked it back up to the PC. I shone light and noticed I can still see my desktop. Does this eliminate a faulty inverter as a possible culprit? Or having removed blacklights still can mean an inverter is bad? I don't have any other inverters to check the backlights that "seemed" to be okay. I have a feeling if it worked, then maybe half of my monitor would have lit up? I also don't have any other backlights to check the current inverter.

My specialty is unfortunately outside of this realm. I'm hoping someone can possibly give me some insight on my issue. Thank you in advance for any pointers.

Additional info: 2 years ago this monitor just stopped working and wouldn't turn on (as in, power button didn't do anything). I have since then stowed it away. Not sure what a time frame of 2 years has done to it sitting in a box.


Well-Known Member
Most Helpful Member
Hy gemisTe,

Welcome to ETO

I see you are from the US- which state?

Yes, it is correct that your monitor back light is not illuminating and that is the problem. The fact that when you shine a flashlight on the screen you can see the correct faint images, indicates that the LCD, the difficult part, is working OK.

These era hp monitors have a history of back light problems. There are some links below giving some more information. The most common problem is poor connections of the wires to the ends of the Cold Cathode Fluorescent Lamps (CCFLs). I would guess that your problem is due to a bad connection on the end of the CCFL that is discolored.

As you indicate, basic broken wires, bad connections etc aside, there are two reasons for no back light:
(1) Inverter failure
(2) Back light failure.

Inverters don't fail that often, but back lights do age and fail. The normal failure mode is a reluctance to strike and illuminate.

As there are two CCFLs behind the LCD screen, if one fails you would expect the other to still work, unless the CCFLs are connected in series, which I suspect is the case.

An inverter for a reasonably large monitor, as opposed to a laptop screen, will probably generate a 1kV semi square wave, so be careful.

You can try heating the CCFLs, with a hair dryer, to no more than 55 deg C and see if they start.

Replacement CCFLs should be available if you need them.


Additional Information

(1) http://h30434.www3.hp.com/t5/Deskto...HP-2509m-monitor-screen-flutters/td-p/1210387

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