On Sun, 19 Jan 2014 16:27:11 -0800 (PST), Chris from London
wrote:

Went to try to fix my daughters ASUS laptop and made it much worse

Welcome to Learn by Destroying(tm).

She did not have her power supply so I used mine - I have an ASUS netbook.
The plug was not the same but the VA are

It's not the power (VA) that needs to be the same. It's the polarity,
voltage, and current rating. The polarity and voltage need to be
exact. The current rating can be higher.

so I rigged up what I thought
was the correct one but when I plugged it in it would not light the
"PSU connected light". Although the laptop worked, without a charger
it was no use.

So, just buy the correct charger and try it.

As it was working before I got my hands on it I assume my connector
somehow caused the PSU circuit to blow. The DC Jack goes to a plug
on the mobo and I tested it in situ - there was 19v at the mobo socket,
so the prob is further down the line.

Offhand, I would guess that you applied reverse power. Please check
and compare the polarity markings on the laptop serial number tag and
the charger.

Here's a photo of the mobo showing the component and the schematic:
http://i989.photobucket.com/albums/a...ps3829aba0.png

I took the liberty of expanding your photo so I could see the
components.
http://www.learnbydestroying.com/jeffl/crud/asus-k501j.jpg
The "hole" in the burnt out component is characteristic of applying
reverse polarity to an active device such as a diode. I would guess
that the diode exploded, blowing the top off the epoxy package.

As Phil notes, there could be other damage. I think this is going to
be an uphill battle and a difficult fix. Good luck.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558