On 03/12/2013 08:33, Chris Bartram wrote:
On 03/12/13 00:30, Lobster wrote:
I have a flatscreen monitor whose (separate) PSU has died and needs
replacing. It's a 12V 3A unit, and as luck would have it I happen to
have
a similar one going spare from a netbook which I no longer have.

Q1: is there any reason why this putative PSU wouldn't be fit for
purpose -
ie is there any other characteristic other than 12V/3A that I need to
consider here?


The polarity of the plug- sometimes the centre is +ve, sometimes -ve.
Sometimes marked on the PSU or the socket on the device it powers.

And sometimes annoying not marked at all on either part. It would have
been nice if there had been a manufacturers convention on polarity and
external diameter used for a given voltage, but it is pretty much
random. Centre positive is more common but there are exceptions

Q2: Assuming we've made it past Q1 - unfortunately the (LV) plug which
connects to the monitor is slightly but crucially differently sized to
the
original, so it won't fit - both are standard-looking concentric plugs
(ie
this sort of thing: http://tinyurl.com/mx35688) but the central pin is
evidently larger on the monitor than it was on my netbook (though the
external diameter looks the same). What are the specs for these
things -
how do I work out what plug I need to buy? I'm assuming it's possible to
buy a solderable version;


Maplin, CPC, or Farnell all sell plugs; they are specified by the length
of the metal connector, it's inside diameter, and inside diameter. It
can be tricky to measure, so you may have to buy a selection.

Allowing for delivery charges Maplin is probably easier for a one off.

otherwise everything I have here is welded
together - is there a neat way of cutting and rejoining the LV flex so I
could recycle what I have? (I wouldn't want to bodge it as I'll probably
pass this monitor on to someone else once it's repaired...)


Probably the neatest way would be solder and heatshrink, but you should
be able to get a solderable plug.

The ID is best measured by finding something like insulated wire or thin
rod that just fits inside and then measuring it that way.

You might need a couple of guesses to get the exact match, some
universal PSUs usually come with a selection of swapable connectors.

--
Regards,
Martin Brown