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Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Not Booting No chime 3 LEDs

Ok so i have a iMac 8,1 with a sensor control problem and the TMoP error (fans on full power, sensor apps don't detect cpu or gpu sensor despite being connected, stay on for about 10 mins) . After looking around it seemed like the logic board. The 8,1 had a much better screen than the 7,1 i have (7,1 was yellowish) so thought id swap it.

Well I went ahead and swapped over the screens ( and while at it the dvd drive too as the 2008 was a bit better)

So first of all I put back together the 'bad' mac (8,1 with the fans spinning and suspected bad logic board).

I fired it up and still with the fans spinning she booted up fine straight into Yosemite albeit with a slightly yellowy screen so I was happy at this point...

This is where it went wrong...

So then I reassembled my 7,1 with the odd and display from my 8,1 that id swapped...

Now it doesn't boot or chime, just the fans spin at a slow speed I only have 3 leds of the 4 lit as well

I then read online this could be a psu fault... its not as I stole that from the other one to test...

i then swapped the graphics cards between the 8,1 and 7,1 8,1 boots just fine 7,1 just has the 3 leds on it still ... im really stuck I don't know whats left except the logic board but I don't understand how I could break it by disconnecting just the lcd temp sensor and the lvds cable ?

Im at a real loss as to what to do now from having two decent imacs less than a week ago I have none any help would be great?

Now I have two imacs by the looks of it both with bad logic boards any ideas what else I could try?

Thanks in advance

Oh yea and now I have put it all back to how it started this morning and still no dice

Answer this question I have this problem too

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You had Yosemite installed and running before the modding - so you met the RAM and HD specs. but you installed an OS that had drivers for one display, then switched to a different one.... poor planning.

The 7,1 Graphics Card may not support the 8.1 display there were two graphic cards for that machine and the "better" screen may also have had the better GPU (since the IDs you provide fit 8 different machines a year apart it's impossible to know, but it could be a reason).

Switching screens may have caused EFI as well as driver issues.

When modding it's best to go slow and make one change at at time and that well researched and prepared. Your Upped your OS, and swapped hardware all in one go... slow down.

Drop back to a box that works... first get the display swap working (sort out any potential GPU/EFI/extension {aka driver} issues), then the optical drive, last the OS.

Lastly you neglected to say which LED is not on. We only know one is dark, and the specif LED points to where your problem can be solved.

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

If this answer is acceptable please remember to return and mark it accepted.

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Hi Machead sorry ... need to give more info... did (sort of ) plan. I checked the 7,1 and 8,1 both have the same ati2600 gpu in (to the extent i even swapped them) the screens also looked pretty much identical.

I tried putting it back to pre me messing with it but still no dice.

The led not working is the 4th one, 1,2,3 are good when power is pressed, 1 only prior to power pressed....

Thanks

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Also have tried a working psu to no avail

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Have you tried connecting an external monitor? If the external worked that would rule out a bad GPU, and if it doesn't there's your problem. There are a number of connectors (connections) that must be correct in order for the display to work. Check them all over for bad connections/connectors. So many times connectors that were "thought" to be "good" were not complete.

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Hi as said before i have swapped the gpu with another one from my other iMac and it works fine and then swapped back and gpu was fine. if i plug the keyboard in the caps lock key won't even light up even after a minute or two it does nothing.

I stripped it and baked the logic board at 375f for 8 minutes but its made no difference its exactly the same...

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