Issues with 21.5" 2011 iMac. GPU or motherboard?

[Marche90]

I originally posted this in the iMac GPU upgrade thread, but now I have realized that I might have a different issue than a bad GPU on my hands.

So, the story is that I bought a cheap 2011 21.5" iMac. Seller said that he started to get pink lines on the display and the iMac wouldn't boot. He took it to a repair shop where he was told that it was a motherboard issue. Issue here is that they seem to have done a shoddy work, since it was missing screws, cables were not properly connected and the IR receiver was missing (HDD is missing too, but that's because the seller took it. Shouldn't be an issue to diagnose the rest of the machine, though). I decided to test my luck and got it.

Today it arrived on my house and decided to test it. When I plugged it I got nothing: no boot chime, no LCD screen, so I opened the iMac, found about the wires and reconnected everything as best as I could. At first I could see on the status LEDs that the 1st and 2nd stayed on, and the fans spun, but I hadn't plugged in the cables of the display. It still did not chimed, however. Left it there for a couple of hours since I had other stuff to do and when I came back and plugged the display back, I could see that only the first LED stayed on. The second LED turns on for a couple of seconds when pressing the On button and the fans start, but a few seconds later they both go off.

I have ordered a new graphics card to test the computer, but it's still a few weeks until I get it. In the mean time, I want to do as much as I can to see if I can at least get a boot chime. Do you think the issue is a motherboard failure, failure to reconnect all the cables in their proper position or a failure on the GPU?... or a combination of everything?

 

[Nguyen Duc Hieu]

I originally posted this in the iMac GPU upgrade thread, but now I have realized that I might have a different issue than a bad GPU on my hands.

So, the story is that I bought a cheap 2011 21.5" iMac. Seller said that he started to get pink lines on the display and the iMac wouldn't boot. He took it to a repair shop where he was told that it was a motherboard issue. Issue here is that they seem to have done a shoddy work, since it was missing screws, cables were not properly connected and the IR receiver was missing (HDD is missing too, but that's because the seller took it. Shouldn't be an issue to diagnose the rest of the machine, though). I decided to test my luck and got it.

Today it arrived on my house and decided to test it. When I plugged it I got nothing: no boot chime, no LCD screen, so I opened the iMac, found about the wires and reconnected everything as best as I could. At first I could see on the status LEDs that the 1st and 2nd stayed on, and the fans spun, but I hadn't plugged in the cables of the display. It still did not chimed, however. Left it there for a couple of hours since I had other stuff to do and when I came back and plugged the display back, I could see that only the first LED stayed on. The second LED turns on for a couple of seconds when pressing the On button and the fans start, but a few seconds later they both go off.

I have ordered a new graphics card to test the computer, but it's still a few weeks until I get it. In the mean time, I want to do as much as I can to see if I can at least get a boot chime. Do you think the issue is a motherboard failure, failure to reconnect all the cables in their proper position or a failure on the GPU?... or a combination of everything?

You don't need to reconnect the LCD to test the logic board and PSU.
Without the LCD, if both PSU and logicboard is good, when powered up, you should see at least 2 LEDs lighting up, both fans spinning.

 

[Marche90]

You don't need to reconnect the LCD to test the logic board and PSU.
Without the LCD, if both PSU and logicboard is good, when powered up, you should see at least 2 LEDs lighting up, both fans spinning.

From what I was reading in an old post, it might be the GPU after all. What is being described in this thread fits exactly my situation: https://forums.macrumors.com/threads/imac-27-2011-wont-boot-up-diagnostic-led-2-blinking.2283009/

Had I found that, I wouldn't have created the thread, but it took forever to dig that one out of search engines, way after posting here.

I still have to wait for the GPU to get here. I just hope it works with an unflashed GPU.

 

[Nguyen Duc Hieu]

From what I was reading in an old post, it might be the GPU after all. What is being described in this thread fits exactly my situation: https://forums.macrumors.com/threads/imac-27-2011-wont-boot-up-diagnostic-led-2-blinking.2283009/

Had I found that, I wouldn't have created the thread, but it took forever to dig that one out of search engines, way after posting here.

I still have to wait for the GPU to get here. I just hope it works with an unflashed GPU.

Your description worried me:
"The second LED turns on for a couple of seconds when pressing the On button and the fans start, but a few seconds later they both go off."

Try removing the GPU to see if 2 LEDs stay stable (they should, if the logic board is good). If not, maybe even the logic board got issue, too.

 

[Marche90]

I removed everything that was not necessary, that is GPU, disk drive, RAM, battery. I get two full lights and a beeping sound (the error when RAM is not detected)... however, as soon as I put in any RAM in any slot (I have 4x2GB sticks) the system goes back to the problematic behavior (LED turns on for a bit then goes off, only one fan spins for a bit then turns off).

I'll first buy another battery and test with it. I'm beginning to think that the issue this iMac has is related to the ram slots, more than with the GPU itself, considering the issues the old owner described, the pink lines at boot and then not booting properly.

EDIT: Eh, nevermind. It sometimes does it even without RAM. Went ahead and bought a new motherboard off eBay. With any luck the original GPU will work, too.

Your description worried me:
"The second LED turns on for a couple of seconds when pressing the On button and the fans start, but a few seconds later they both go off."

Try removing the GPU to see if 2 LEDs stay stable (they should, if the logic board is good). If not, maybe even the logic board got issue, too.