I have the same problem - not working touch screen, but mine voltage is only 4.7 while screen is on. It is pipo m2. Maybe you can contact the seller again, so they would tell you what to replace in this case?
I think the Pipo M2 and M3 have the same motherboard, so she way to repair the touchscreen should also be the same.
try other diode, I used 1N4148, and you should install it with correct polarity, which is shown on the picture above. Also, don't forger to use the insulating tape after installing the diode.
Hope, this helps.