5 replies to this topic

[sargentim]

Hey all,

Had my XDA IIs for about a month now and i've noticed a high pitched whining noise coming from the unit.

On closer listening, it appears to be coming from the centre of the screen and NOT the speaker.

When the screens on, the noise is present. If i hold the screen down, the noise dissapears, but re-appears when i release.

Is this a common fault? Or is it a fault at all? My ears cant take much more of this whining!

If it is a fault, where can it be repaired? I think it may be out of warrenty....

[fraser]

Many of them make a sound, I'd imagine that some are louder than others. It's probably the high-voltage dc-dc converter in the screen that's doing it; uses all sorts of high frequencies and electrical trickery to power the backlight.

As it changes when you press down, yours could be worse than others. Dunno where to fix it though; is it that bad?

[fluffcat1]

fraser, on Mar 6 2006, 11:22, said:

Many of them make a sound, I'd imagine that some are louder than others. It's probably the high-voltage dc-dc converter in the screen that's doing it; uses all sorts of high frequencies and electrical trickery to power the backlight.

<{POST_SNAPBACK}>

It's not high voltage ( the backlight LEDs run at 19v according to my un-calibrated fluke meter ) and the conversion is done on the board not the LCM. HTC haven't used high voltage backlights since the screens in the wallaby / iPaq 36XX generation.

Richard

[fraser]

Interesting, shows you how long it's been since I disassembled a TFT-style screen!! Are laptops the same nowadays?

[fluffcat1]

fraser, on Apr 5 2006, 16:24, said:

Interesting, shows you how long it's been since I disassembled a TFT-style screen!! Are laptops the same nowadays?

<{POST_SNAPBACK}>

I don't think the LED's would emit enough light to cover a laptop screen? The LCM's in PDA's use LEDs with a translucent 'transmission layer' of plastic to spread the light behind the panel. I'm surprised how uniform the backlighting looks actually.

Funnily enough I'll have a 1.5 yr old compaq NX9010 screen in bits in the next few to sort a dry joint so I'll check the voltage. My compaq TC1000 tablet PC ( 3.5 yr old design ) has a step up convertor offboard near the screen but it's older technology.

Richard

[fraser]

Yeah, all the laptops I have (and have opened/repaired) at at least three years old and they all have the HT backlights via a little dc-dc converter, always mounted in the screen (to allow a low voltage link to the main components I presume). These always whine to some degree as far as I'm aware.

I think I measured 500V once, but it may have been around the 300V mark (it was 8/9 years ago). I'm still weary of these things, despite  having had so many shocks you'd think I'd be used to it by now. At least it's not CRTs!