screen not working after a replacement? there are plenty of causes for it.
Before starting, look for the following;
- All connectors are in tact. (no tears, disconnects, and clean)
- The battery is re-installed. (commonly the battery gets left unplugged on home repairs)
- The computer reads the device. (plug it in, itunes should recognize it as a locked device)
- There is no physical damage to the board. (scratches, missing/chipped components, etc)
1) Start with a redo. Open the device, Disassemble it as needed, and reconnect everything. something may be causing issues.
2) try a hard reset. (plug it in, and hold the power button, and the home button for a minimum of 15 seconds) see if you see the apple logo.
3) if this doesnt work, you could have a backlight issue. Shine a flashlight onto the screen and see if you can get a dim picture. if you see the outlines of your background, then you may have a backlight issue. in this case, start by trying to resolder the three connections on the top of the back of the screen, that leed to your backlight.
4) should these not be the case, you could have a bad screen. it happens often. at my store, we always try three before moving forward with other possibilities.
5) this point forward, you are likely looking at a board level issue. boards are usually not worth replacing, but if you can reflow some components, you may be able to get it working again. set your hot air rework nozzle to approximately 300-325, and airflow to medium. heat up the board localized around the screen connectors and see if the connectors are working.