On Fri, 19 Dec 2008 07:07:11 -0800 (PST), wrote:

On Dec 19, 2:25*am, mm wrote:
On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:





mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. *Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

Yes, 3 pins. It's a Targus, like the ones in the url you posted in
reply to Tony.

BTW, it turns out not all Targus tips will fit all Targus adapters.
They have indents and things to keep that from happening. I bought
this adapter for a friend and then his old Macintosh broke, and I
thought I could use the adapter for myself, with a tip I had, maybe
from an AC-only adapter. But the tip wouldn't fit in the other
adapter. I forget the details, but my friend bought a later model Mac
and the second tip fit it, so I gave it to him and everything is
fine.**

If you buy one of these things in the store, and it's opened all
ready, check for the tip you need before you leave the store. I had
bought one early on that was missing one tip.

**Then I fixed his old Macintosh. He got an image of a floppy on the
screen which meant the system was't on the harddrive or the harddrive
had failed. I took it apart according to the directions in the
manual, and I couldn't get the harddrive out to look at it, but while
trying, I disconnected it a couple times, and when I reassembled the
thing, it worked. It was all screwed together when this started. I
don't know how the connection went bad.

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark