Dave Inscribed thus:


"Dave" wrote in message
netamerica...

wrote in message
...
On Thu, 28 Oct 2010 09:41:01 -0500, "Dave"
wrote:

Appears (to my eye) to have a faulty voltage regulator on the
motherboard,
but where? 19.5 VDC input from the AC adapter, but only 1VDC
(slightly less
actually) available at the Power On switch (which I would expect to
have at
least 5 VDC). Anybody have any idea how power is handled for these
critters? Model 305CRV. Can get SN if necessary. I somehow
expected to find something like a LM317, or at least a couple of
7805/7905 combinations.
Shows what I know about laptops. Any help is appreciated...

Thanks,

Dave


I would expect some type ofswitch mode power supply - they're
available as a single chip with minimal external components. Much
more efficent than the 'room warmers' like the LM317/78xx devices.

Check for questionable electrolytic capacitors - a dead one can kill
the switch mode power supply.

SMPS don't like caps with high ESR either - probably easier to
replace than to test.

John

Hey, THANKS John. I will definetly check this out. Much
appreciated.

Dave



Hey John, took a look at the motherboard again with no (obvious) luck.
One question: would the there be a SMPS on the motherboard, in
addition to
whatever is in the AC adapter? I have the voltage from the AC adapter
coming into the board, but it does not appear to be "processed" into
anything like a 5V supply for the digital logic to operate with. It
seems
to simply drop to the 1VDC level I mentioned earlier. I feel like I
ought to be able to locate the source of the trouble, but haven't been
able to do so.

Thanks,

Dave

There are maybe half a dozen SMPS in a laptop ! You need to trace the
19V to find out where it goes. Not at all easy, even if you have a
circuit diagram !

--
Best Regards:
Baron.