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zoran

macrumors 601
Original poster
Jun 30, 2005
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As I was working on my 27” mid2010 iMac, the computer froze and its screen changed with strange graphic artefacts.​

I shut it down and after a min when I tried to power it back on again, it just wouldn’t start.​

When I pressed the power button to turn it on, I could hear the fans starting to work, but after 5secs they stopped.
No chime was heard, nor would the iMac boot. Screen remained black.

I have no clue what my next step can be… I’m totally lost, what can i look for in order to know what could be wrong?
 
It sounds like you may have experienced a graphics card failure. It could also be caused by other things such as a defective power supply.

If you have another Mac you might want to try Target Disk Mode. Or you could try booting the iMac from an external hard drive.
 
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One more thing is that, underneath, next to the memory modules, I can see 3 green led lights when I power on the iMac. And when it’s powered off, only one led light still remains lighted.
Might this perhaps say something about the defective or not powering?
Regarding Target disk mode, i only have a MacMini with USB2 ports and one FW port... can it work with that?
 
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zoran said:
One more thing is that, underneath, next to the memory modules, I can see 3 green led lights when I power on the iMac. And when it’s powered off, only one led light still remains lighted.
Might this perhaps say something about the defective or not powering?
Regarding Target disk mode, i only have a MacMini with USB2 ports and one FW port... can it work with that?
Click to expand...

3 lights with a black screen means a recognized GPU which couldn't drive the LCD (half dead), or bad LCD (not very likely). PSU is still OK.
If your iMac 2010 is still equiped with its stock GPU, then the highest chance is the GPU.
How to test (troubleshooting):
Open your iMac and remove the GPU (it's removable)
Power it on again (w/o the GPU and LCD) and do a PRAM reset.
It should chime and its fans should be running fine (work in Target Disk Mode).
 
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- Why a half dead LCD? Due to the fact that the GPU isn’t working?
- Yes it’s equipped with the stock GPU. (By the way is it best to replace it with the same or make an upgrade to a diff one? I think there was an upgrade for the GPU back then)
- What’s a PSU?
- To remove the GPU and power it on, means I’ll have to place back the display? w/o means without?
- How do I do a Pram reset? And why do it?
- No idea how to work in Target Disk mode
 
zoran said:
- Why a half dead LCD? Due to the fact that the GPU isn’t working?
- Yes it’s equipped with the stock GPU. (By the way is it best to replace it with the same or make an upgrade to a diff one? I think there was an upgrade for the GPU back then)
- What’s a PSU?
- To remove the GPU and power it on, means I’ll have to place back the display? w/o means without?
- How do I do a Pram reset? And why do it?
- No idea how to work in Target Disk mode
Click to expand...

- Full dead GPU => Only 2 LEDs lit up
- It's best to replace with the same one.
- PSU = Power Supplying Unit
- w/o = without
- Press the button, and within 1s, press and hold Command + Option + P + R on the keyboard.
- Once you have open the iMac, forget Target Disk Mode. No data need to be retrieved.

Remember to UNPLUG the iMac before disassembling.
 
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Nguyen Duc Hieu said:
- It's best to replace with the same one.
- Press the button, and within 1s, press and hold Command + Option + P + R on the keyboard.
- Once you have open the iMac, forget Target Disk Mode. No data need to be retrieved.

Remember to UNPLUG the iMac before disassembling.
Click to expand...
- Which GPU is the one I’m looking for?
- Are u 100% certain that it’s the GPU?
- What exactly does a PRAM reset?
- Will I loose any data? Why shouldn’t I use TDMode? What was it for in the first place?
 
zoran said:
- Which GPU is the one I’m looking for?
- Are u 100% certain that it’s the GPU?
- What exactly does a PRAM reset?
- Will I loose any data? Why shouldn’t I use TDMode? What was it for in the first place?
Click to expand...

- HD4850 for iMac
- No I am not. It's your iMac, not mine.
- a PRAM reset tells the machine to re-scan the whole system for changed parts.
- Do you have any data to loose?
Take the HDD out, put it to an USB enclosure and connect it to another Mac to retrieve your data.
USB is more popular than the Firewire which is needed for your iMac to work in Target Display Mode.
 
- you are absolutely correct, im sorry if i sounded weird asking you if you were "100% certain", i didn't mean to, im already grateful for your help.
Im just wondering if other than you suggestion to take out the display and GPU will make me certain if i hear the chime and the fans working that the issue is the GPU
- regarding the data, well since ill open the iMac to remove display and GPU, ill remove the drives too, i do have a TMachine backup on everything though
- do i need to make a PRAM reset when ill remove the GPU to test it?
 
zoran said:
- you are absolutely correct, im sorry if i sounded weird asking you if you were "100% certain", i didn't mean to, im already grateful for your help.
Im just wondering if other than you suggestion to take out the display and GPU will make me certain if i hear the chime and the fans working that the issue is the GPU
- regarding the data, well since ill open the iMac to remove display and GPU, ill remove the drives too, i do have a TMachine backup on everything though
- do i need to make a PRAM reset when ill remove the GPU to test it?
Click to expand...

- What I meant was: without the machine in front of my eye, I can't be sure 100%. (only >90%, though).
- I'm not very sure, but unplug the machine from the power, then after 15s, plug it back in again may get you the chime you expect. (My iMac 2009 once got into this situation when its GPU was dead, had to unplug-replug to get it boot and chime again)
- You don't need a PRAM reset, but it's a good practice when making changes to the machine.
 
its very hard to place back -to the mainboard- the GPU temp connector, cause the connector is underneath and not visible
 
zoran said:
its very hard to place back -to the mainboard- the GPU temp connector, cause the connector is underneath and not visible
Click to expand...

You are supposed to take the whole set out before assembling the GPU (MXM card).
If you still want to handle the GPU without remove the logicboard, here are some tips:
1. Use a hard plastic card to separate the frame from the logicboard. I didn't and knocked off a transistor on the logicboard. Had to re-solder it back for the LCD to display image.
2. Use a pair of twitzers to handle the GPU thermo sensor.
3. Loosen several screws on the logicboard will help handle the GPU easier.
 
just to do the testing, is it ok if i leave the sensor on and do the boot? or must i remove the sensor anyway?
 
Removed the GPU
Didn't remove the GPU temp sensor
Connected the keyboard
Did a Pram reset
Fans are working at high speed
I heard the Chime (what a great feeling to hear it)
What do i do now? :)
 
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Ive placed the GPU back in and i hear a continuous chime sound.
Ive also placed the display and the continuous chime is still there at boot.
Did a PRAM reset with the display but the Continuous chime is still there.
Might that mean thats its the card thats creating the things, or perhaps i did something wrong at placing the card or else?
 
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After a few hours, when i removed the GPU, the continuous chime went away.
But its strange, if its the GPU causing the continuous chime, why wasn't it there in the first place, before i opened the iMac and before i removed/connected the GPU?
 
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There might be some change in the circuit when you removed and re-assembled the graphic card.
Continuous chime sound means you've got a boot loop, causing by a short circuit in the graphic card.
Anyway, as you have detected that the graphic card is the issue, just discard it.
It's time to think about what to do with the 27" iMac.

- If you still want to use it as a computer, replace or upgrade the graphic card.
- If you want to re-use it as a 27" display, replace the whole guts with an LCD driver board.
 
Nguyen Duc Hieu said:
- If you still want to use it as a computer, replace or upgrade the graphic card.
Click to expand...
I don't know what gr.card i should be looking for. Its a 27" mid 2010 core i7 iMac, SerialNo:CK0410H8DNR EMC:2390


Nguyen Duc Hieu said:
- If you want to re-use it as a 27" display, replace the whole guts with an LCD driver board.
Click to expand...
What exactly will this do, can i place a Retina screen?
 
zoran said:
I don't know what gr.card i should be looking for. Its a 27" mid 2010 core i7 iMac, SerialNo:CK0410H8DNR EMC:2390
Click to expand...

HD5670m for iMac
HD5750m for iMac

zoran said:
What exactly will this do, can i place a Retina screen?
Click to expand...

No you can't. iMac 2010 doesn't have retina screen. It's just a common LED lit LCD with TN panel.
The LCD driver board will convert your dead iMac to a stand-alone display. It will have common ports like HDMI, DP, VGA input to receive video signal from other PCs or Macs.
 
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Hi guys... im begging to be depressed again. After a couple of months of using the replacement graphics card, im experiencing the following issues. Every now and then the display either goes full white, or black or a color of some sort. It was red the other day. I have to do a restart so that i can be able to work again... what should i do? This is something that occurring after 2-3 months of use.
 
zoran said:
Hi guys... im begging to be depressed again. After a couple of months of using the replacement graphics card, im experiencing the following issues. Every now and then the display either goes full white, or black or a color of some sort. It was red the other day. I have to do a restart so that i can be able to work again... what should i do? This is something that occurring after 2-3 months of use.
Click to expand...

The GPU is dead, again?
You can try Apple Diagnostic to see what's wrong.
But the only thing you have changed recently is only the GPU, so it's just common sense to guess that the GPU is bad.
 
Apple Diagnostic? Where is that and what exactly will it trace?
 
After pressing D after startup it went on some Internet mode searching for a long time and i didn't know what to do....
 
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