iMac 27 Black Screen Driving me mad but external ok?

[rickce]

Hello,

I have an iMac and it’s driving me mad….. It starts up and chimes The screen is black but lit. I have put a torch right up to the display and can see nothing.

I have took the mac to tfix and they have done the following:

After replacing LCD cable and LCD connections the issue was still present.
We have attempted GPU reball, which has not resolved the issue.
We have purchased and installed new updated GPU chip after installation the original fault was still present.

I ordered a graphics card before I took it to tfix and it arrived whist it was being repaired.

Before I fitted it I connected an external monitor to the imac and I got an output, see the attached picture (not sure what it has booted in to? can anyone advise? I could dim the brightness of the display when I used the volume keys on the keyboard I had sound. I then swapped out the graphics card and it was the same with no output.

I am thinking the display is faulty? Or maybe logic board but then I am getting output to an external monitor?

I also put a drive in it that I disk imaged from a working mac, and checked the image worked via usb boot and it booted to OSX, and same screen and no boot to OSX, I could right click and got another menu but that was it…

Any ideas direction would be appreciated.

Thanks,

rocl

Mac Details:
Mac 27" Processor: 2.66GHz Core i5 (750)
Model #: A1312
Model Family: iMac Processor: 2.66GHz Core i5 (750) Manufacturer: Intel # of CPUs: 1 Codename: Lynnfield Display:
Size: 27" Finish:
Glossy Resolution: 2560x1440
Graphics: ATI Radeon HD 4850 (512MB)
Sales Number(s): MB953LL/A
Machine Number(s): iMac10,1 D
Production: Oct 20, 2009 - Jul 27, 2010
Factory: China Production
Year: 2010 Production
Week: 18 (May)
Production Number: 1659

 

[tatarin]

Hi,

I have the same MB953 A1312 27" iMac although it was manufactured in November 2009 and I purchased it on 19 Nov 2009. So I have had it for almost exactly 4 years.

Several months ago the backlight started to turn off when the computer got hot. The LCD still worked (visible with a small high intensity flashlight) and I could screen share from another computer. For a while, putting a powerful fan behind the computer solved the problem but eventually the backlight would only stay on for a few seconds even after a cold start.

I took the computer to the Mall of America Apple store for repair. At first, they thought that the problem was the backlight board (part 661-5311; $78.41 + $39 labor). However, replacing the board didn't solve the problem.

So then they replaced the entire display (part 661-5527; $510.23 + $39 labor). I just got the computer back several days ago and it seems to be working fine now. I didn't have to pay for the unsuccessful backlight board replacement.

I hope this is useful.