Ok, with (nearly) nothing to loose, I decided to take the plunge and rip the iPronto apart.
Arm yourself with a T6 Torx screwdriver, and earth yourself on a metal casing (or even better, use an earth/ground strap)
Remove the battery and network card and remove the 5 screws shown -
Start from the bottom near the battery and pull the casing away (use your fingers to save leaving rectangular screwdriver marks along the edge of the casing).
It's worth noting that the blue trim stays with the front of the unit -
Lift the backing outwards and back to disengage the clips shown -
Two either side, sorry for the quality of the RH side pic
With the iPronto face down and the right way up, carefully prise the backing upwards and push away from you to disengage the 3 clips along the top -
You're in !
The top (or back) circuitboard has two screws at the top and a clip holding it at the bottom...
...and looks like this when removed -
There's a push-fit connector concealed under the foam on the right-hand side
and this is as far as I got - I thought maybe the touchscreen ribbon cable (highlighted above) may have come out, so excitedly re-connected everything ... had a heart-wrenching moment when it wouldn't power up after plugging in the A/C adaptor, then remembered I'd unplugged the adapter from the mains to earth myself through an amplifier casing ... powered it up - still no reaction from the touch screen.
I suspect either the ribbon's damaged/cracked where it joins the screen, or there's something more serious going on in the circuitry.
Anyway, hope this is of some use to anyone worried about taking their unit apart - there's nothing to it !