Official Touch Screen not powering by microUSB any more

Hi I bought an official 7" touch screen for my PI earlier in the year and for some reason its stopped getting power via the microusb port. I have to use a separate powe rsupply for it via micorusb as I have the main pi connected to a HifiBerry amp which powers the amp and pi via 12v supply but its not supported to power the screen as well. I can get it to power up via the GPIO connections but as mentioned its not supported and tends to be very unreliable as the power is restricted by nature of the amp. Any ideas? Would this be covered by its warranty?