Do you have a multimeter? You can look for the fuses on the motherboard and check the continuity. I don't know where they are on that motherboard, some high resolution photos would be helpful.
It would also be helpful to mark where exactly you put the knife on the docking connector when you saw the spark. On page 187 there is the pinout of the connector http://h10032.www1.hp.com/ctg/Manual/c01122797.pdf
and we can guess what was broken by the short circuit.

Hi,

Yes I have a multi meter so doing some continuity tests shouldn't be a problem.

Here are some high res images.

1. Damaged docking connector. You can see where it is bowed and this is where I ran the penknife blade through.

2. Bottom side of the motherboard - docking connector is top right

3. Underneath the plastic sheet where the docking connector is soldered to the board

4. Top side of the motherboard - sound chip is top right (ESS Alegro)

5. WIth DC/DC converter removed

6. Other side of the docking connector

You could check components marked F and L for continuity. You could also try measuring the voltage on VCC pin of sound chip, to see if it gets any power when the board is turned on. But here you would need to be careful too, in order to not cause more damage by touching multiple pins. Maybe the VCC pin is connected to a nearby capacitor, and you can check the voltage on that capacitor, which would be easier.

No continuity problems. I also removed cpu heatsink and fan and found a couple of extra fuses but these check out ok too. Guess I will try the VCC on the sound chip itself next.

Some progress. This bus controller IC gets really really hot - too hot to touch after a few minutes of the motherboard being powered up. Given its proximity to the docking connector that would seem to make sense however I'm not sure if the fact it is getting hot is because it itself is shorted internally and needs to be replaced or if it is the victim of a short elsewhere.

I'll source a replacement anyway and try to desolder.

You might look for shorted capacitors (tantalum, ceramic). But maybe it is a problem with that IC. If you have hot air station you can desolder it, if not you can carefully cut the pins with razor (near the body of that IC) and desolder them one by one. If a replacement IC is cheap.

I desoldered the chip using the second method, cleaned up the pads and the laptop is happy to POST without it and does now reboot properly when exiting the BIOS. Reading the IC specs I think this is simply a bus connector for the docking port so I may well be able to get away without a replacement as I don't plan on using it that way.

Now to re-assembly. I took the all of the plastic sheets off the various parts of the motherboard. They are pretty disgusting to I'll probably cut some replacements but does anyone know what kid of adhesive to use - sticky but not permanent sticky.

Thanks in advance.