A mid-2010 iMac for free

[DeltaMac]

You won't know if you get working external video, until you test it...
I am only offering suggestions for things to test.
and, I am guessing that if you do get external video (and your iMac will probably boot then), you may then be able to state that your graphics card is likely OK.
Then, you work your way down the short list that I offered in post #44, starting with the LED backlight board, and going on to the LCD panel.
What's after that? the logic board.

 

[zoran]

Regarding the LCD panel, I connected a display controller board and the panel was working fine… so I guess thats out of the way… do you agree?

 

[zoran]

I removed the gpu, started the iMac and there was no chime/boot loop heard... its seems that it was the gpu causing the issue! Would you say that this indicates 100% that im dealing with a bad gpu?

 

[DeltaMac]

So, you connected a different backlight controller? and then you get video?
So, the problem is the backlight controller, I would think.
(Did you forget to say if the reboot problem was still there with the replacement controller?)

 

[zoran]

Have u read my post in #53 ?

 

[DeltaMac]

Yes, post #53 is a different troubleshooting step, with a different result, correct?
I was asking for clarification of your step of replacing the controller.
You DID say that you plugged in a (replacement? or same ? ) controller board. So, you got video, and, by extenstion, I can assume that you could boot. Is that accurate? That's what I was asking about...
The #53 post was, IMHO, trying to boot iMac without a video output, where you did not get chime/boot... But, then you have no video at all. I don't think you can then assume that the GPU is the issue, just from that. The best way to rule out the graphics card, is to swap in a known-good graphics card.

 

[zoran]

Regarding the display controller board (don’t know if it’s called "backlight controller board") I mentioned it so we could rule out that a faulty display might of been the issue.
By uninstalling the gpu, I wanted to see if without it I would still experience the chime loop!
So… there was no chime

 

[DeltaMac]

Yes, that should also tell you that your iMac won't boot without a video card (the GPU).

You said the LCD panel worked OK after connecting a "controller board". You still didn't say that the controller board allowed your iMac to begin to boot, so, did it get further into the boot sequence (video on, visible elements on the screen, if only the Apple icon? )
(You may call that board anything you like, but Apple calls it an "LED backlight board", or simply "backlight board".

 

[zoran]

Im sorry but I don’t understand. Whats there to boot with the use of this controller board (cb)? The specific cb, just turns the iMac as a display, makes the iMac as a monitor. All the rest of the iMacs hardware can be left out. There is no boot sequence with this board. I only used it for specifying if the display is faulty or not.
Also, the fact that there is just one chime when booting without the gpu, doesn't that indicate that the gpu was the cause of the looping chimes? I also installed an older faulty gpu (stock) and there was a chime loop as well.

 

[DeltaMac]

Im sorry but I don’t understand. Whats there to boot with the use of this controller board (cb)? The specific cb, just turns the iMac as a display, makes the iMac as a monitor. All the rest of the iMacs hardware can be left out. There is no boot sequence with this board. I only used it for specifying if the display is faulty or not.
Also, the fact that there is just one chime when booting without the gpu, doesn't that indicate that the gpu was the cause of the looping chimes? I also installed an older faulty gpu (stock) and there was a chime loop as well.

I apologize. I misinterpreted your post where you said you connected a controller board, thinking you meant that you swapped in a different (identical) backlight board, (and i did not suspect that you installed one to try the display, not connected to the iMac's internal electronics.)
So... after thinking on that, I would probably also conclude that the video card (the GPU) is probably not contributing to the boot loop. And, I am more suspicious of the backlight board, and then on to the logic board.

 

[zoran]

Plz plz plz, i never said this for you to apologize! Are u kidding me? You have helped me so much in this and many other issues, that you should NOT apologize! ❤️
Anyway... here is a thought. If there was a chance that the backlight board or the logic board, were faulty, shouldn't there be a chime loop still occurring after the gpu's removal? Since the chime loop didn't occur after the gpu was removed, isn't that evidence that the problem is the GPU?

 

[DeltaMac]

OK, without actually looking at your iMac, and trying a few things, I can't really disagree with your suggestion.
But, I do know that the video, logic board, other bits such as the backlight board, and, of course, the power supply, all work together for all those various functions to, well, function.
(My suspicion is that the system can't boot successfully if the video card is removed. That is, your iMac won't POST, so you don't get a chime in any case when the video card is not in place.)
Maybe I have the wrong idea, and someone else will point out the error in my thinking.

Finally, if you want to move ahead with getting your iMac to work again, try replacing the video card first, then, in whatever sequence, swap out the backlight board, the logic board, and the power supply.
Something will fix it. Maybe you will get lucky the first time.