[PLUG] Possible fried laptop...

Keith Lofstrom keithl at kl-ic.com
Mon Dec 22 06:10:02 UTC 2008


On Sun, Dec 21, 2008 at 06:38:53PM -0800, Eitan Tsur wrote:
> Hi all,  so I lost power for a couple hours today, and my laptop was on
> during the outage.  I shut it down, plugged it in, and waited until the
> power came back to use it again.  Since then the power has come back on,
> however the laptop will no longer POST, and the power light flashes.  This
> has never happened before, (light flashing or no POST condition,) and seems
> to be unaffected by being on wall power or not, with or without the battery
> installed.  If anyone has any thoughts on what could cause this sort of
> situation, please let me know.

The first thing to check is whether the AC adapter produces the
right voltage.  It is difficult for a power line upset "reach
through" the AC adapter and zap the laptop.  If it somehow did,
it is even more unlikely for the adapter to produce normal
voltage afterwards.  There is a lot of power regulating circuitry
in most laptop adapters, and I would expect that to blow first.

However, what CAN happen is that the line power can bounce on and
off in the wrong way, the output of a poorly designed adapter can 
bounce up and down with it, and this can stress the power input
circuitry of the laptop, wreaking havoc.  This should not happen
with well designed power hardware.  Sadly, at most places I know
about the power supply is where they save pennies on components,
and save salary cost by hiring second rate engineers.  Power
supply behavior under funny line conditions is a not banner spec
or a driver of purchasing decisions.  I have seen two battery
charging circuits fail on 1997-era laptops, necessitating depot
level repair.  IBM was great for these fixes, Levono not so 
much, Dell used to suck horribly.  But things change.

If it is a zorched power supply on the laptop motherboard, the
whole motherboard will need replacing.  You will have a hard
time isolating and identifying the blown semiconductor (s),
figuring out the part number, and finding a replacement for sale
somewhere, because they probably don't manufacture it anymore.

That said, Google is your friend.  Look to see if others have
had the problem with your model number.  And eBay is your friend;
a lot of people break screens and other components that aren't
the motherboard, so you can usually find used replacements cheap.

My bet on the broken component is (1) AC adapter, (2) battery,
(3) motherboard.  It helps to have spares for (1) and (2) anyway.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs



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