Thanks to another member purchased a spare TB IC in the post.

Easiest to remove them by snipping all the pins off the chip , then mop up the solder and pins off the PCB.

Mounting new IC is straightforward, it clips over the board and holds itself inplace whilst soldering.

Unfortunately in this case , didn`t entirely solve the problem, Z fine going down, stalls and whines going up, hmmm

Transfer to Y axis , whines, lack of power.

PCB back under the magnifier, toasted thin ground track from what looks like 1R0 current sense resistor, put wire in from nearest pad to ground pin.

Result, fully working Z axis driver board.

Just one wiring anomoly now, must have reversed ppahses because motor is runnig reversed, up is down and down is up, do I have to get the soldering iron out again or can I reverse it in Mach3?

Cheers
Adam

P.S. Also contacted vendor, who has asked for a picture of the damaged board so that they can send me out the right spare part under warranty, have just repaired in meantime to keep running.