At normal viewing distance, my Dell U2410 monitor is now completely silent at low brightness settings. I accomplished this by drastic surgery on the LCD panel casing.
LONG VERSION
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The Dell U2410 24" monitor emits a loud hum when the brightness is set below about 78. Above about 83, it is quiet, but way too bright and emits a lot of heat. I couldn't live with this situation, so I disassembled the monitor to find and fix the source of the noise.
When I opened the monitor, I found three sources of sound. The main power-supply board and the inverter board both emit a faint hiss that I could not hear when the monitor was assembled. The loud buzzing you hear when the monitor is assembled comes entirely from the LCD panel.
The largest PCB in the monitor is for the power supply. All the transformers on this board are well potted and emit only a faint hiss that you can hear from a few inches away.
To the left of the power supply is the inverter board. The 7 transformers here are not potted and do buzz. However, the monitor case is enough to contain the sound. I potted these transformers with epoxy just to see what would happen, but it had no effect, since the epoxy couldn't get into the cores.
The LCD panel is an LG panel module LM240WU4. Since the humming is caused by the pulse-width modulation method used to dim the brightness, I spent several months experimenting with ways to mechanically isolate the components of the LCD panel to determine how each interaction contributed to the total noise. What I found is that most of the hum is caused by the proximity of the CCFL lamps to the aluminum casing of the panel. Mechanical isolation of the lamps from the frame did not eliminate the hum. Ultimately, the only way to eliminate the effect was to cut out the entire back of the panel casing. I cut away the entire back of the back panel, leaving a frame with three little bits where the inverter PCB mounts. With the CCFL lamps in position but not physically mounted, it was perfectly silent. When the lamps were pressed into their mounts, there was some hum, but little enough that it is blocked by the monitor case when all is assembled. I experimented with flexible mounting that gave some mechanical isolation of the lamps from the frame, but found it wasn't worth it.
TIPS ON DISASSEMBLING
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I couldn't find any instructions for this online, so here are some tips to help you avoid disaster.
* You open the monitor case by removing the front bezel. Start in the middle of the bottom edge to hide any scratches. Using something flat and firm, press the bezel toward the center of the screen until you feel the lip come free from the catch, then pull it out toward you. I used toothpicks to keep each latch from falling back in as I worked my way around the frame.
* Once you have the plastic case removed and the unit is lying face-down (on something really soft!) the metal covers over the PCBs mostly remove easily. In my monitor, the top screw holding the cover over the inverter board was glued fast. If yours is too, don't try removing it with a screwdriver. I had to use pliers from the other side, with nearly enough torque to break the screw. That was the only time I had to apply significant force to something.
* Once the frame holding the circuitry is removed, you have to take the back off the illumination panel. It's tricky to figure out; stop if you find yourself applying force. First, remove the small piece of tape on the lower left side of the inner frame. Then, starting at the bottom and working up the sides, pry the catches on the inner metal frame loose from the plastic middle frame. I used little plastic paperclips to keep the catches from falling back in. Once the bottom and sides are free, hinge it open along the top. Don't ever poke into or exert force along the top edge; there is circuitry in there!
REPLACEMENT CCFL LAMPS
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If you break a CCFL lamp, Dell will tell you to just buy a whole new monitor. The only place I know of to get a replacement lamp is CCFL Warehouse. http://www.ccflwarehouse.com/
The correct lamp for the U2410 is the "530 mm U Shape CCFL Backlight Lamp - 3.0 mm Diameter", code U5302730.
Be careful to get the right size. They seem to not always have it in stock, and may substitute a model that is 30 mm (U5303030) wide instead of the correct 27 mm (U5302730). (They did that to me the first time.)
Be warned that the CCFL Warehouse lamps are distinctly inferior to the originals. The color is a bit warmer, but I can't see the difference in the display. The real problem is that their lamps have an oddly short shelf life. If they are left unused for several months or more, they lose the ability to fully illuminate. When you light them up, they look like a nearly dead lamp, illuminating only up to about 7 inches from the leads, even with the monitor at high brightness. If you leave them going for several hours, they gradually get brighter, but it seems they never regain their full brightness. I called CCFL Warehouse and was told that they were aware of the issue but that any dissatisfaction I might have with their product was none of their concern.
How I silenced a Dell U2410 monitor
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee
Re: How I silenced a Dell U2410 monitor
Nice, but too complicated for me to do 
rather sell the u2711 and get something elze xd.
I like my ccfl very much, only recently discover the hum with a new silent pc.
My u2711 stop humming at 79-80 mark. I lower the brightness with the rgb gain, (with a calibator). I don't really mind the heat, but using lcd to block the brightess kill the calibated contrast from 650ish:1 to 300:1. Uncalibated contrast is 900:1, so it is kind of "old". It serves as a secondary now, so I gonna leave it alone until I find another use for it.
Tbh, I thought I was insane when I first heard the hum. Life is so hard for people who are over-sensitive.
rather sell the u2711 and get something elze xd.I like my ccfl very much, only recently discover the hum with a new silent pc.
My u2711 stop humming at 79-80 mark. I lower the brightness with the rgb gain, (with a calibator). I don't really mind the heat, but using lcd to block the brightess kill the calibated contrast from 650ish:1 to 300:1. Uncalibated contrast is 900:1, so it is kind of "old". It serves as a secondary now, so I gonna leave it alone until I find another use for it.
Tbh, I thought I was insane when I first heard the hum. Life is so hard for people who are over-sensitive.
Re: How I silenced a Dell U2410 monitor
baii, might be a bad version. My U2711 doesn't hum and I always thought the backlight's brightness was voltage controlled, or least with a very hight frequency PWM signal.
Re: How I silenced a Dell U2410 monitor
It is only audible at relative close distance in absolute silence or if I tip my ear on it. As I said, I only noticed it recently with new build, and my old laptop is not loud at all, Just slight ambient whoosh when idle.Cistron wrote:baii, might be a bad version. My U2711 doesn't hum and I always thought the backlight's brightness was voltage controlled, or least with a very hight frequency PWM signal.
It is high frequency pwm like most ccfl, easily seen using a phone camera.