Got a nice phone (Xiaomi Mi A1 aka Tissot) which suffered from the touch screen not recognizing touch in a band across the screen. So I purchased a replacement screen (with frame) from Aliexpress and... didn't get around to fixing it - didn't want to end up with a part-dismantled phone, and the touch thing was mostly able to be worked around. But eventually I did replace the screen and it all worked great! Except GSM. Seems that I didn't connect the tiny coax connector properly, so took it apart again to fix that and managed to crack the screen.
Got another screen off Aliexpress and this one shows how cheap they are being. The ally frame fixing tabs needed work with a needle file for the PCBs to fit, but otherwise it went OK and it works. Kind of. The display is washed out and needs brightness turned up high, and it is not as sharp as the original (or replacement, or a second one of these I have). So... yep, you guessed, ordered another screen from a more reputable, but still Aliexpress, store. This one looks good - the packaging is much more professional, the battery sticky tabs are in place, etc. And that's how we get to my question (sorry, thought the history might help fend off some questions):
On power up the boot logo shows as normal, and the screen is lit up (albeit not at full brightness, but that's normal). Then that screen goes and the Android animated logo should show, but the screen is blank. If I get a torch and shine it on the screen I can see the LCD is indeed working, it's just that there is no backlight. Obviously, the backlight is bust in some way. But... it works for the initial power up so it can't be broken.
Anyone got a clue as to how this could occur? I switched back to the previous frame and screen and that doesn't exhibit the issue, so it is something to do with this particular screen, but it works to start up...