I have had this problem several times on the same phone, I let it sit for 2-3 days with the logic board out of the phone. I found on my last install when my customers power switch would not work properly:

1. Disconnect the #4 cable and tilt the motherboard up so it does not contact the battery.

2. Connect all the connectors for the face.

3. set the motherboard down on the battery.

4. Connect the #4 cable and the LCD worked properly.

Shut down the phone properly and reinstall the motherboard screws

Good luck

plug it in to itunes and restore that worked for me

Use recboot to put yr device into restore mode then use it to exit restore mode, y take back yr screen without making a complète restore

Once the screen would light up faintly but stay black, we called the iphone and when it lit up faintly again, do a 10 second hard reset while it is still lit up and the apple will appear, and the screen will come back on-back to normal

All, Thanks for the feedback I appreciate the kind words.

Rob,

At this point I would disassemble the phone completely, primarily remove the front assembly and motherboard. Let the phone sit for 5-10 min, then reassemble. While you are waiting read through the teardown for your phone and familiarize yourself with the connections, but here is how I would reassemble:

1. Place the motherboard in with something propping it up off of the battery connections.

2. Connect the LCD, Digitizer and ear speaker(cables 1, 2, and 3)

3. Connect the On/off ribbon cable and the GPS antenna Cables 5 and 6.

4. Remove the object propping up your phone and set the motherboard on the battery connection install the screw holding it down on the battery.

5. Connect the Charging dock and Wi-Fi antenna(3Gs only) (cables 4 and 7)

When the phone boots up normally, shut it down properly, remove the front assembly and install the rest of your screws.

Try this a few times and if it still doesn't work I would say the ribbon cable needs to be addressed.

Hope this helps!

I've got the same issue. I've restored the phone and it completes it goes into DFU mode and it vibrates at times but there's no picture. The phone LCD is completely dead. I've taken it apart disconnected and reconnected the wires and I've had no luck.

I did notice while I was in the phone that the #4 conector wasn't connected after I did a complete restore to custom firmware. Now I don't think it came loose when I popped the screen loose so this has me interested.

when you take apart an iPhone 3G/3Gs... do not forget to turn it off before you take it apart. it usually in a way "tricks" your motherboard into thinking your LCD is on when it is not, and and when it is all together your LCD is black. so don't forget to turn it off before you start the repair..

had same as above problem (black screen on reassembly) after replacing the complete 3 part lcd screen, digitizer / button assembly, i got mine working by holding both the on/off button and the front screen button on or down together, the apple logo came in view and the problem seems to be rectified, leaving it on charge over night and all so far seems ok, seems that i did not power off properly as other people mention but, i couldn't due to the damage sustained with it being thrown at me in a row with the enemy at home!, lol.

Thank you very much this was extremely helpful! I had the same issue with my iPad 2. I replaced he digitizer and my LCD seemed to stop working after I replaced the cracked screen. I assumed that I had cracked the LCD during the removal of the screen. I purchased a new LCD but it still did not work. After reading your answers, I realized what the problem was. I turned off the iPad and then turned it back on and vuala it worked just fine.

Guys I have the same problem but can not understand what Steve is asking me to do. I replaced the power button circuitry and now I just get a blank screen with the occasional vibration from it. I have a faint back light though. Which one is the 4 cable and what does he mean but tilt it away from the battery. Do I tack the motherboard completely out again and disconnect all the wires??

I'm ver confused and very fustrated

Can someone pleeeease help ?

Thanks

Rob

Thanks Steve, I did what you said but to no avail. Eventually I gave up and a local repair shop charged me £15 to make sure I put it all back together correctly. I had but what i had done was when i unscrewed the power putton on my iPhone 4 i bent the digitizer cable right back instead of folding it in half to get to the screw. This was why the screen was not working. I sorced a new one locally for £25 and it now works fine. So big tip guys........ to unscrew the power botton housing fold the digitizer cable in half, NOT right back on itself.

Hope this helps others !

Thanks

Rob

Thanks a lot ;-)

I installed a program and it got frozen, reactivation with power home,

but stays on the startup logo.

Could not turn off, nor DFU or whatsoever.

So opened the iphone to check home button and in doing so disconnected the LCD.

After reassembly this resulted in a black screen.

Now I've got the startup logo back and that is an improvement :-)

And now the rest, but that will be another story

Thanks again for thr help !

Have a nice day.

Dorian

Hi there i have a iphone 3gs that has the black screen but when u plug in to itunes it makes the ding ive tried every thing u guys have said should i get another screen cause i have 2 lcd i have tried and nothing happens ??? need help ????

i swear just plug or connect your iphone to itune and restore after installing the new screen it work for me

OK!

I have been through all of this and here are my answers:

1. If you accidently turn on an iPhone before connecting the display the LCD is off when it should be on

2. The EASIEST fix is to download the software called 'Tiny Umbrella'

3. Once you have installed the software just click enter recovery and then exit recovery and bingo your phone should turn back on