Chosen Solution
I hope someone can help. I have been on the case of my iMac late 2009 (27 inch) for over a week now. At the end of the robe here (and possible fixes found online and in the manual) The issue: screen went black and although the computer power on the screen never really gets going. It is not black black but appear to have some light going but I can not see anything.tried solutions: troubleshot and fixes from the official manual for this model. This includes connecting external monitor which works all fine (so not the video card). I can work from the external monitor as per usual. Testing if all 4 led diagnostic lights comes on as expected (they do). Checking cables connecting the lcd screen, and I cannot find any immediate issues. And of course all the suggested resets (SMC, PRAM etc.) . Flashlight test (i cant see anything at all). And the Brightness is set correctly. I have attached a picture of what the screen looks like (Sorry for the less than great quality - difficult to capture) The manual suggested a next step to be to replace the backlight board (but someone noted it was only likely to be the issue if i could see the Apple logo very very faintly when turning the computer off (i dont see anything). Another next step potential fix from the manual is a new LCD screen. However, that will be too costly at this point I think - especisææy given that I might not be the issue. I just really liked the computer and it worked very well until now. I am grateful for any further insights! thank you so much for your reply. I have added pics. Hope it is was pics like these you were requesting. thank you! I also tried to take a video with an inspection cam, but the metal shines back too much. Perhaps I will try again during daytime tomorrow.
@lisbethl according to your images, the backlight does come on. That means your monitor does not receive any video or can’t display it. This could be an issue with the LVDS cable but it could also be an issue with the logic board, power circuitry and the T-con board. We would need to know exactly what 820-xxxx your board is. In the abscences of knowing your logic board version, I would suggest that you measure the voltages on pins 27-29 on the connector at the back of the monitor. Here you should get 12V and on pin 30 you should get 3.3V. All voltages are of course DC. Pin 22-25 on the connector are ground. Careful that you do not shorten the pins out. Let us know what you get.
I suspect your LVDS cable connector is bad on the logic board or the cable was put in backwards which burnt some of the logic near the connector. Take some good detailed pictures of the connector so we can see it straight on and down wards where the cable is inserted and post them here for us to see Adding images to an existing question Update (10/09/2018) OK! I see the problem! The connector is damaged! The shield is lifted a bit on the Left side You can try pushing it down so it doesn’t short the ribbon cable contacts. The 2nd to last picture makes this clear. Often I see the connector yanked forward on the Right side so the connector it’s not parallel with the logic board which is also the case here as well. Note the gap difference on the left Vs right in the last picture. The LVDS cable is a bit short so its easy to pull on it causing damage to either the cable or the connector. I don’t think reforming the connector will fix this as the tension within the connector pins is not assured. I end up just replacing the connector.
