In my experience the red flash is usually a nand issue. I have resolved it by pulling the nand from the board and formatting it and then doing a DFU restore. I just received a new lot of A1701/A1709 10.5’s and I’ve come come across one that is still wrapped in the plastic, perfect condition, and it shows the red flash before the screen turns black. The first attempt to restore the device saw the progress bar get near to the end of the restore before failing and rebooting into recovery but now every subsequent attempt results in the red flash before it even gets to the part where the progress bar appears. I was hoping I wasnt going to have to remove the plastic from this one but it looks like I’m going to have to crack this thing open. I’ll update once again to advise if a simple nand replacement/wipe did the job!
You probably wont find a “replacement part” but you should easily find a broken display with the cables still attached. I usually snip the redundant cable where the connector protrudes from the inner layers and then grab a display out of my junk pile, pry it open, steal the cable and then retrofit/adhere it to the shield on the back of the display.