Noisy component in the Dell U2410

[wenp]

Dell U2410 monitors (not all?) hum loudly when the brightness is reduced below about 78%. Dell claims this is not a defect, but the nearly identical U2711 does not have this problem.

I have a Dell U2410 rev. A04 with the LG panel module LM240WU4. When I opened the monitor, I found there to be 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 appears to be within the LG panel, on the right side, just where the middle CCFL tube terminates.

Getting into that area would be a lot more work. Also, I wouldn't be able to run the unit to produce the noise. Any ideas on what the problem might be or how to test it?

One thing I did consider is a bad component on the inverter board. With extra wiring, I swapped around the CCFL tubes to different transformers. The noise always stayed in the same place.

Also, I'd appreciate any info on how the relevant parts of the U2711 differ from the U2410.

Thanks

[wenp]

Re: Noisy component in the Dell U2410

Silence...

Could somebody at least describe what is typically found inside that part of the panel unit?

Is there a service manual available for the U2410?

[Th3_uN1Qu3]

Re: Noisy component in the Dell U2410

Seen this before on a few other monitors - it's likely the CCFLs themselves making the noise.

Due to manufacturing tolerances one of the lamps touches the screen frame. Because the PWM dimming is done at low frequency (typically 120Hz), this may cause the lamp to vibrate, this is then transmitted to the frame and casing, resulting in an objectionable buzz noise.

[Krankshaft]

Re: Noisy component in the Dell U2410

Wouldn't it also be possible that the inverter transformer secondary windings are vibrating?

[wenp]

Re: Noisy component in the Dell U2410

Wouldn't it also be possible that the inverter transformer secondary windings are vibrating?

I understand that is sometimes the case. Here, I had carefully checked for sound and vibration from the transformers on the inverter board. They emit only a faint hiss and I can't detect any vibration.

[alexanna]

Re: Noisy component in the Dell U2410

I understand that is sometimes the case. Here, I had carefully checked for sound and vibration from the transformers on the inverter board. They emit only a faint hiss and I can't detect any vibration.

You may have to,Dissemble one Panel down to the metal frame and the CCFLs channels. Then just plug in the CCFLs to see if you can isolate the noise.

[Th3_uN1Qu3]

Re: Noisy component in the Dell U2410

Wouldn't it also be possible that the inverter transformer secondary windings are vibrating?

Unfortunately in my experience it's been more often the lamps than the inverters. The inverters or power supply can be quieted by brushing on a layer of clear lacquer and allowing it to dry before the thing is re-assembled.

[wenp]

Re: Noisy component in the Dell U2410

...it's likely the CCFLs themselves making the noise...this is then transmitted to the frame and casing, resulting in an objectionable buzz noise.

This turned out to be approximately the case.

Inside the panel is very simple. A thin plastic bracket along the side of the back holds in place a series of rubber sockets. The back side of each socket takes a prong from the inverter board and the front side takes a CCFL lead. I guess the main source of the noise is the bracket transferring vibration to the aluminum back.

I doesn't look like there is room for any vibration damping material. Not sure what I'm going to try.