[mdlug] Laptop Hardware issues

[Raymond McLaughlin]

One of the subjects that the discussion turned to at today's meeting was
this poor dead laptop. The discussion started
here:<http://mdlug.org/pipermail/mdlug/2009-February/006448.html>

Robert Meier wrote:
> Raymond McLaughlin wrote:
>> Michael Rudas wrote:
>>> Robert Meier wrote:
>>>> I suspect a bad power supply.
>>>
>>> As someone who has repaired hundreds of switching power supplies, I
>>> agree with Bob--the power supply is likely defective or marginal,
>>> probably a bad electrolytic capacitor.  ...
> 
>> By power supply do you mean the brick that I plug in the wall?
> 
> The power supply in question is the component that the "brick"
> plugs into on the laptop side.  It is likely to be an aluminum box
> with the socket to plug the "brick" into and several ribbon/zip
> cables with only 2, 3, or 4 conduits each.

Here is a picture of where the round power connector plugs into the
laptop:<http://mdlug.org/contacts/president/scripts+scraps/images/p1010042.html>
Not much in the way of components there. (The other side of that circuit
board has no components at all, save the plastic plug with the power
out.)  Also I doubt that any of these components are the source of the
problem, the battery charged with out problem. And when running (or
trying to run) off battery these parts aren't in the circuit.
Here's another shot that shows the cable that takes the power to the
mother board, it's the square plug.
<http://mdlug.org/contacts/president/scripts+scraps/images/p1010038.html>

And in this shot
<http://mdlug.org/contacts/president/scripts+scraps/images/p1010036.html>
you can see the white square connector that takes that square plug. Just
above that are the 6 tines that connect into the battery. I don't see
anything in this vicinity that looks like a "switching power supply"
such as you have described. Those "R45X 7126Q" components could be solid
state DC/DC  converters. Here's a better look at how they look at how
they are attached to the board.
<http://mdlug.org/contacts/president/scripts+scraps/images/p1010045.html>

It looks like a kind of tricky solder job, and I have no idea where to
get replacements. Just googling R45X and 7126Q separately finds  nothing
useful, and both terms in the same search finds nothing at all.


>  It is also likely
> to be a section of the motherboard, with the socket soldered
> to the motherboard, and larger than average traces in that area.
> In either manifestation its purpose is to isolate the computer
> (high-gain) circuitry from fluctuations due to varying load
> or line (brick) noise.

I would expect a modern "brick" to have pretty good noise suppression
built into it.

> 
> The computer circuitry only needs clean steady voltage,
> so attaching the motherboard feed lines to a "bench supply"
> will demonstrate whether or not the laptop power supply
> is indeed the problem.

Again I'm pretty sure I'm supplying the motherboard with steady, clean
power when I try to running from just the (fully charged) battery pack.

> Replacing the coil, diodes, or capacitor is usually an easy
> solder job, as they normally need only be "big enough" not
> "tuned".

Interestingly there isn't a single "can" type capacitor on the whole
board. Any power handling capacitors must be solid state. I'm not sure
what thet look like, but I think that's a couple of them just to the
right of the CMOS battery connection, with the distinct "+" signs on
them.
<http://mdlug.org/contacts/president/scripts+scraps/images/p1010052.html>

> Good luck,


Any more ideas?

Ray