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Laptop wil not power on.

 
 
Steve
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      07-13-2007
Compaq Presario m2000 Notebook will not power on. Battery is charged
and light on AC supply light is on. Removed battery and tried AC
only, no luck. Same with Battery and no AC. Tried power supply and
AC from second m2000 and also tried bad parts on good m2000.
Everything checks out OK on good machine.

If this was a desktop I would say power supply, but notebooks don't
have power supplies?

Any ideas?
 
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Paul
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      07-14-2007
Steve wrote:
> Compaq Presario m2000 Notebook will not power on. Battery is charged
> and light on AC supply light is on. Removed battery and tried AC
> only, no luck. Same with Battery and no AC. Tried power supply and
> AC from second m2000 and also tried bad parts on good m2000.
> Everything checks out OK on good machine.
>
> If this was a desktop I would say power supply, but notebooks don't
> have power supplies?
>
> Any ideas?


Something has to convert the 12V or whatever comes from the adapter,
into the lower voltage used by the ICs. The battery is probably
in the vicinity of 12V or so as well.

This "pico" converter gives an idea how tiny the conversion circuit
can be. This one passes the 12V through without modification, and
makes 3.3V and 5V from the 12V input. These are used to power mini-itx
motherboards from a wall wart adapter.

http://www.mini-itx.com/store/?c=10#picoPSU

In the laptop, you might need 5V for the USB interface. I'm not sure
how many chips really need 3.3V any more - 3.3V is certainly a popular
voltage for chips having CMOS interfaces. But maybe not a lot of amperes
are needed for 3.3V.

The current consumption on some of the lower voltage rails can be
more substantial. 1.8V, 1.5V, 1.3V are examples of some voltages that
might be used. The processor circuit needs quite a few amps, which is
why it is usually a multiphase converter.

For efficient conversion, anything that uses a lot of current, should
be supplied by a switcher. Components common in such things, are MOSFETs
for switching, a "donut with wire on it", and capacitors.

Usually, there will be the concept of "power good" with the conversion
process. Each converter will play a part in a logic signal called
"power good", and when all converters are at their operating voltage,
the "power good" signal will indicate to the logic that it can start
running. Lack of such a signal, could indicate that one of the converters
is not happy.

When a converter suffers an overload, at least some of them latch off.
To get a circuit like that to recover, worst case you might have
to remove all power sources (in a laptop, that would be both the
battery and the AC power source). Then, when you reapply power, the
circuit will try again. If a conversion circuit is weak, or it is
being overloaded by something, it could fail to start each time you
try it.

Since I haven't seen a reference schematic for a laptop, I cannot
really say more than that about it. It should share some concepts
with how other computers are powered. Naturally, more efficient
implementations should be used, to give better battery life, and
keep the internal temperature of the laptop down.

In the picture here, it looks like a major part of the power
conversion, is in the upper left part of this picture. The components
will look different than a motherboard, as they are selected for
smaller size. In fact, that only thing that looks familiar, is the
CMOS battery

http://www.notebookparts.com/images/...368-001_tn.jpg

The likely answer you'll get, is "new motherboard" and a big bill,
if you take it somewhere. That is the beauty of notebook/laptop
computers - they are a definite "profit center", for whoever
works on them. I can imagine their staff, sitting, drooling by
the phone, waiting for people to call and ask for their expensive
services. (That "$200 just to look at it" thing.)

Good luck,
Paul
 
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