4 
2 Diagnose Display or Video problem?
iMac Intel 27" A1312 EMC 2374 i7
iMac powers on and chime sounds, the display can be seen to power on and remains black the entire time, checked with flashlight and nothing is seen.
All of the LED's are lit, I can connect to the unit remotely and share the screen, I checked the system profiler and find that the video card is detected. I find that if I go to the display preferences and adjust the screen brightness you can see the backlight adjust as its supposed to.
I tried reset all settings
I tried re-seating the video card
I tried swapping backlight inverter and LCD with Known good hardware same result
video card is my last step but i just wanted any suggestions before i shell out the cash
thanks
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Just an update, after re-checking all cables and connectors I found V-Sync LCD Cable broken in half hidden under the tape, I ordered the replacement and will update when I replace it.
(And yes it seems I always end up with video issues even after upgrading...gave the 20" to dad:-) ).
из junvaz
I replaced the cable and still get the same result here is what the system report tells me...I will try any other suggestions, otherwise I will roll the dice and order a replacement video card.
Chipset Model: ATI Radeon HD 4850
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 512 MB
Vendor: ATI (0x1002)
Device ID: 0x944a
Revision ID: 0x0000
ROM Revision: 113-B9110C-425
EFI Driver Version: 01.00.383
Displays:
iMac:
Display Type: LCD
Resolution: 2560 x 1440
Pixel Depth: 32-Bit Color (ARGB8888)
Main Display: Yes
Mirror: Off
Online: Yes
Built-In: Yes
Connection Type: DisplayPort
из junvaz