[JasonACT]

I've had the USB stick connected for almost 7 years (I bought it for the car) so probably not a slow thing. Just an extra load on the components though, where in fringe circumstances it's probably best not to have it.

It's possible the broken unit I have just had a "bad USB day" one time, the difference I see is to the port itself and I've got nothing connected on either boards on the workbench so it shouldn't make a difference.

I'm still checking components, I think I've done all the resistors now - every one of them is the same resistance on both boards.

I'm going to have to get my logic analyser out and start recording power-up details of the various chips which have pins exposed. There's also microSD tracks on the circuit board (no actual socket though) but I'll plug that into the analyser to see if both units attempt to read SD cards.