iMac Intel 27". EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz), EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz)

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iMac 27" black lit screen

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 a UK computer repair center and they have done the following:

Replaced the 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.

We have tried to source replacement GPU card however none of our trusted suppliers had any in stock.

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

I put it in and now I have an output on an external monitor and I get the OS-X desktop. I can dim the brightness of the internal display and when I used the volume keys on the keyboard I get sound.

I also bought a new display from ebay but its the same just black and illuminated (however that could be faulty also?).

I can't see how this is a the logic board failure if I can use an external monitor?

Any help would be appreciated thanks

Rick

Answered! View the answer I have this problem too

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Rick - Can you give us the last three digits of your serial number so we can correctly identify your system. Once we have that we might be able to help.

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Hello, yes sure it's 5PJ

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Yes here is the full spec

Thanks,

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

Memory: 4GB PC3-8500 SODIMM

Max Memory: 16GB #

Graphics: ATI Radeon HD 4850 (512MB)

Base Storage: 1TB 7200RPM SATA 3.5"

Optical Drive: 8x DL Superdrive

Model Number: A1312

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

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So how was it. Did you fixed? I also have same problem.

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2 Answers

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If I understand things here correctly you had replaced the connector on the original graphics board and now you have replaced the graphics board with a new one. Likewise you have replaced the LCD unit as well.

At present you have no problems using an external monitor (new graphics board & LCD). So we know the issue is Between the LCD panel and the system but where?

You have replaced the LVDS cable, correct? So we know it can't be that. So that leaves us with two cables and the thermal sensor.

We know the back light is working as you can see it glowing. We can use a sensor & fan monitoring software application to see what the sensor is doing.

  • I like Temperature Gauge which you can down load from the App store but any app like it will work as well here.

So lets assume you have checked the thermal sensor and it is working, that leaves the vertical sync cable or the power supply as the problem here. Can you make a careful inspection of the cable and the connectors to see if there is any damage? If you don't see anything do you have a spare power supply you can swap out to test things, hopefully this will identify the problem as a power supply issue.

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@Dan, just following it out of curiosity. I am missing the part of the working backlight.....

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Second sentence 'The screen is black but lit.' Keep me honest OT ;-}

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It's all good;-)

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Hello Dan,

Many thanks for this! :)

I will try that.

I had changed the cable from the logic board to the screen (LDVS cable) the one that provides the video.

Yes connection between the LCD panel and the system.

I will give temperature gauge a go and see what it says.

When you say vertical sync cable do you mean the LVDS cable? I do have a new one I have not fitted as the repair shop fitted one also.

Also when you say power supply, do you mean the inverter board?

Yes the screen is back lit and I can control the brightness with the F1 & F2 keys, so would that indicate that power is ok?

Thanks for all the help!!

Rick

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Review Step5 in this IFIXIT guide iMac Intel 27" EMC 2309 and 2374 Display Replacement. This is the Sync cable which connects to the power supply {what I think you describe as an inverter}. In Step6 the LED backlight cable is removed from the same power supply.

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As I have the same problem since this morning: Did this solve the issue Rick? I know it's been over a year now, but this is exactly what I was looking for the whole day. :-)

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I suspect the LED driver died.

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Thank you for the answer Dan!

My case for the posterity:

I don't have the exact same problem as above.

Screen was completely black, didn't see anything. It did wake up for a split second after a PRAM reset but went black again. Every 10th or 20th reboot, it woke up and worked fine.

It happened that the display woke up on reboot, the Apple logo and progress bar showed up, but went black when it was at 1/4.

Well, somehow the LCD doesn' wake up.

When the int. display did wake up, I was able to mirror the screen onto an ext. display which worked normal. No problem here.

put the mac into the sleep mode and woke it up. Ext. display OK, internal display stayed black. Reboot. Tried it again and the int. display woke up. Boom. Just like nothing ever happened.

I set the brightness somewhere <50% and rebooted it. Voila, the display woke up. Since then everythings OK but I haven't tried to set the brightness >50% and reboot. I'm kind of scared now. ;)

Hope this helps anyone.

iMac 27" (late 2009), Yosemite 10.10.2

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Rick C will be eternally grateful.
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