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 Post subject: Power Saving for Display Component Longevity
 Post Posted: Fri Jan 27, 2012 1:45 am 
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Joined: Sun Feb 07, 2010 2:47 pm
Posts: 94
Hi Scott-

I was just reading in "Upgrading and Repairing PCs" on page 896 the section about power cycling.

I've been running my ThinkPad T40p off of one of those little 12V to 120VAC power converters in my car. It has a little wattmeter on it. The meter reads in graduations of 1 Watt. So I figure if it reads 0 that means its drawing less than .5 a Watt.

I've noticed that when the laptop is idling and I set the screen to go blank that it draws 0 Watts, which I find kind of hard to believe. But I haven't got any reason to doubt it.

Anyway, one thing that this says to me is that the screen (for this particular laptop) draws most of the power.

Now I haven't read "Upgrading and Repairing Laptops" yet. But I've read a little bit about them in other books. According to my understanding the screen is lit by a backlight that is something like a flourescent tube. And it is powered by something called an inverter that jumps the DC battery voltage up to the high voltage that the backlight runs on. I suspect it works in conjunction with some type of transformer.

Now I would think that the backlight is sort of analogous to a light bulb just like semiconductor materials. To keep the thermal shock down you could leave it on as long as possible.

But what about that inverter and the transformer that works with it. It doesn't have any moving parts it it. It's probably made of some kind of switching semiconductor or transistor circuits. So maybe the light bulb analogy works for it. Does it work for the transformer part of the circuit as well?

If it doesn't I'm curious to know how difficult it is to replace the inverter. Is it something built into the motherboard? I've heard they are sometimes built into part of the display. Also, I wonder if they are available new for older computers? Can they be bought new indefinetly? There are pretty much unique for a particular model laptop aren't they? There has to be a time when a manufacturer stops support for a particular model of laptop.

I guess the question I'm curious about here is: if I want the display components to last as long as possible, do I want to leave the display on all the time or off all the time?


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 Post subject: Re: Power Saving for Display Component Longevity
 Post Posted: Fri Jan 27, 2012 10:59 am 
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Thermal shock/cycling does indeed reduce the life of both the backlight and the inverter, so anything you do to reduce the number and severity of the thermal cycles will make those components last longer.

Quote:
...this says to me is that the screen (for this particular laptop) draws most of the power.

That is true, the screen is by far the most power hungry device in a modern laptop, accounting for more than 40% of the total power draw in most systems.

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...I'm curious to know how difficult it is to replace the inverter. Is it something built into the motherboard? I've heard they are sometimes built into part of the display.

Inverters are usually mounted somewhere in the LCD panel (usually at the base of the lid in a laptop), and are specific to the LCD used.

While they are somewhat failure prone, fortunately they are easy to find, relatively inexpensive, and easy to replace. Because they are a failure-prone component, they seem to be available long after a given laptop has been discontinued.

Note that newer laptops use LED backlights that don't use an inverter and have a significantly longer life than CCFL backlights, plus they also consume about 10% less power.


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 Post subject: Re: Power Saving for Display Component Longevity
 Post Posted: Sat Jan 28, 2012 12:18 am 
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That answers my questions, thanks. Especially for all those good links.


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