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Can anyone help me in solving this issue? The iMac is starting up: I can hear the chime The display stays blank (it is completely off), the external display connected through thunderbolt port and hdmi cable says no signal. I opened it: The 1st and the 2nd led are on when the internal display is connected The 1st, the 2nd and the 3rd led are on when the internal display is disconnected Internal battery is 2.85V The OS seems to start when internal display is not connected as the wireless keyboard power on and seems to be connected The fans run full speed An assistance manual suggests to replace the display port flat cable, or the GPU or the logic board. Before wasting money, I would appreciate some suggestions from you. Thanks you in advance. Update (09/13/) I took some pictures. They are not very clear (tomorrow I will try with a microscope) but it seems to me there is some problem on the male connector at logic board side. What do you think about? calbe pictures Thanks in advance Raffaele Update (09/15/2015) I finally was able to take some pictures at the microscope, I added them to the shared collection linked in the previous message. The cable ending at board side showed a little bending which I was able to fix, the last two pictures refer to the fixed connector. After connecting again everything it worked for a while: all 4 LEDs were on and the display showed the gray apple and the progress bar. But after a few seconds the display and the 4th led turned off again. No signal, everytime, to the external display. Should I perhaps apply any special procedure to activate the external display? I also noticed that after a few minutes of trials, booting and shutdowning, also the 3rd led goes off. Now, whatever the display is connected or not, only 1st and 2nd led are on. I really don’t know what else doing. Please, help me. Thank you in advance Raffaele Update (09/16/2015) The 4 last digits of the Serial No. are: DHJF Model is EMC 2428. When I got the video signal (it was for short) the external display was connected (thunderbolt port to HDMI adaptor) but no signal was detected by external display. Moreover, with 3rd LED off or on the external display never gets a video signal. Update (10/18/2015) After trying a hot air reflow on my GPU, this is the updated status of my iMac: After start up and chime sound, third led seems to be on stable over time I can connect via ssh to the Mac, logging as root. The content of the hard disk seems to be integer. But the led panel is completely off. Now that I can log into my iMac, is there anyone who can suggest me what to look for to understand why the led panel is off? Thank you Update (10/18/2015) Hello everybody, I updated my post as now the iMac seems to be working but no video signal is present at all.
If the both the internal & external displays don’t show any life and the external is correctly connected. I would say the internal display cable was put in backwards. The diagnostic LED #3 is telling us the logic board & the graphics card are communicating so I don’t understand it being off when you have the internal display disconnected. As the LED #4 is not lit that would imply the internal display can’t be seen. Yet you also tell us you can’t get an image on the external. So you may have bad graphics board here as well. Take a clear set of pictures of the cables end and the boards connector so we can see what we have here and post them in your question. Update (09/19/2015) At this point I think you’ll need to replace the graphics card. Here’s the Apple P/N: 661-5944 AMD Radeon HD 6750M w/512MB
