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lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
Got a used 2010 21.5” iMac, turn it on, can hear apple chime sound, but no display on screen (completely dark), but system boots up OK with external monitor connected. Removed the display assembly and check all cables there, they seems fine, and the connector on logic board seems OK too. So, how to check if the issue is from logic board or screen assembly itself? Any thoughts?

Thanks,
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
If the image is OK on an external display, then you can assume that the video circuitry on the logic board is working.

Turn on the iMac, shine a bright light into the screen. Do you see any kind of image, even though the screen is quite dark (indicating that the backlight is not working)? That could be the LED backlight board.
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
If the image is OK on an external display, then you can assume that the video circuitry on the logic board is working.

Turn on the iMac, shine a bright light into the screen. Do you see any kind of image, even though the screen is quite dark (indicating that the backlight is not working)? That could be the LED backlight board.
Tried it with the flash light, but can't see anything. Could it be the connection pin on logic board is broken? Is there any simple way to detect it?
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14

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DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
No way to tell anything, as the actual connector contacts are not visible from that angle.
Even if you could see something wrong, there's no practical way to fix that, other than simply replacing the logic board.
However, if there is a fault somewhere, it would more likely be the ribbon cable that uses that connector.
Apple's part number for the ribbon cable (the DisplayPort cable) is 922-9497.
Here's one: https://www.amazon.com/Display-Ribbon-Compatible-593-1280-922-9497/dp/B07W4J8W21

But, there is no way to tell if the cable will change anything, or if it will help. But, it's fairly easy to swap another cable, and give it a quick test...
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
No way to tell anything, as the actual connector contacts are not visible from that angle.
Even if you could see something wrong, there's no practical way to fix that, other than simply replacing the logic board.
However, if there is a fault somewhere, it would more likely be the ribbon cable that uses that connector.
Apple's part number for the ribbon cable (the DisplayPort cable) is 922-9497.
Here's one: https://www.amazon.com/Display-Ribbon-Compatible-593-1280-922-9497/dp/B07W4J8W21

But, there is no way to tell if the cable will change anything, or if it will help. But, it's fairly easy to swap another cable, and give it a quick test...
Good point, will try that, thanks!
 

Fishrrman

macrumors Penryn
Feb 20, 2009
28,735
12,846
It's not worth it to put too much money into a 12-year-old iMac, particularly a small-screen model...
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
Here is the update for the diagno0stic, light 2 on logic board is not on after turning it on, I can see and hear the fan running (both for optical and cpu), but no Apple chime sound, tried several times, same thing, does this mean the PSU is faulty? Any thoughts? Thanks!
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
Will the iMac shut off (fans stop running) if you hold the power button for about 10 seconds?
If so, press and release the power button, and hold Command + R (to boot to recovery mode)
Do you see anything on the screen?
If you shine a bright light into the screen, is anything visble, even though the screen might be nearly dark?
I know you checked for that earlier, but double-check this.
I think more likely the logic board is faulty, but could still be the power supply. The power supply would be easier (and cheaper), so if you want to try replacing a part, the power supply would be a good first choice -- and logic board would be next. (Could be both ... )
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
Will the iMac shut off (fans stop running) if you hold the power button for about 10 seconds?
If so, press and release the power button, and hold Command + R (to boot to recovery mode)
Do you see anything on the screen?
If you shine a bright light into the screen, is anything visble, even though the screen might be nearly dark?
I know you checked for that earlier, but double-check this.
I think more likely the logic board is faulty, but could still be the power supply. The power supply would be easier (and cheaper), so if you want to try replacing a part, the power supply would be a good first choice -- and logic board would be next. (Could be both ... )
Actually, it stopped working with no chime sound and no more images displaying on the external monitor few days after my initial post(but it can still be turned on with fans running). I thought the logic board might be dead, so I bought a logic board over ebay with pretty good deal, and have the logic board replaced, however, it is the same symptom that it can power on with fans running, but no chime sound, no images out (both on screen or external display), checking those lights on logic board, only the first light is solid and others are off all the time, replaced the PSU with one I removed from a 2011 imac 21.5" (not sure if it is in working condition), but something, so, I'm curious to know what else could be wrong here?
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
Just to verify, you say that both the internal display, and an external display (with a connector cable that you are sure is good) -- neither display will show anything except a black screen.?
If not the power supply -- and you tried a logic board. (just to make sure, the power supply is, in fact, the same on both the 2010 and 2011 iMacs.)
Another item that would affect power is the DC power cable (Apple's part number 922-9125 )
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
Just to verify, you say that both the internal display, and an external display (with a connector cable that you are sure is good) -- neither display will show anything except a black screen.?
If not the power supply -- and you tried a logic board. (just to make sure, the power supply is, in fact, the same on both the 2010 and 2011 iMacs.)
Another item that would affect power is the DC power cable (Apple's part number 922-9125 )
Right, neither display will show anything except a black screen. From the diagnostic diagram for those 4 lights on logic board, it seemed that it should be the PSU if the 2nd light won't turn on at all, but since I tried both PSU but got the same result, it' not likely the reason. Also, I tried the different power cord, and no difference either. This is kind of puzzle to me. One thing I noticed today is that, the cpu fan runs quietly at the beginning, but became very loud afterward, does it indicate anything here? Thanks.
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
The DC power cable is not referred to as a "cord". It is an internal cable that connects the PSU to the logic board.
The logic board has to be removed to get at one of the connectors.
Is THAT cable the one that you tried already?
If you have a replacement logic board, did it come with the video card --- or did you transfer the video card that was already installed to the second logic board?
If not, did you try swapping the video card from one logic board to the other?
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
The DC power cable is not referred to as a "cord". It is an internal cable that connects the PSU to the logic board.
The logic board has to be removed to get at one of the connectors.
Is THAT cable the one that you tried already?
If you have a replacement logic board, did it come with the video card --- or did you transfer the video card that was already installed to the second logic board?
If not, did you try swapping the video card from one logic board to the other?
Got you, will try that power switch today, I haven’t thought about it, but if that component failed, should the first light remain off too? By the way, The new logic board doesn’t come with GPU nor cpu, so, I have to remove them from the old board.
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
The PSU has to provide a sort-of "Boot voltage", or would be called a trickle-voltage. If that part of the PSU is good, then the #1 will always be on whenever the power cord is connected to AC power.
The second LED should come on immediately after pressing the power button. That would tell you that the PSU is connected to the logic board, and the logic board has responded by turning on that #2 LED.
As you have only the one graphics card (the GPU) that you have swapped when changing the logic board, and you don't get anything on either the internal or external display, then I suspect that the GPU is not working. That's also probably why the #2 LED is not coming on (logic board has to work, and the GPU is attached to the logic board.)
You should try a different video card. Hopefully, the logic board is not going to be an issue (a bad part, such as a video card, might cause other failures on the logic board itself, so you could have two bad logic boards now. One way to test that, is to try a known good video card.)
 

lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
Thanks for your detailed explanation. If I understand it correctly, the failure of GPU May cause logic board malfunction and not communicate with PSU correctly, thus, the 2nd LED light won’t be turned on as it supposed to be, right?
 

DeltaMac

macrumors G5
Jul 30, 2003
13,589
4,485
Delaware
It's possible. On other Macs, I have seen video problems because of a problem in the PSU (perhaps not enough power available to turn on video)
But, as you have fans working, and no chime, you have some power, and you said that you tried a different PSU, and swapped in a different logic board. You have a major component left, which would be the video card.
You have a lot of effort (and some money) in an older iMac, and, at some point, you get to decide if more time and money is worth the result.
You have seen a couple of posts offering the opinion that a 12-year-old iMac is not worth much, so you shouldn't waste your money. I tend to disagree with that viewpoint, as I am a stubborn enough to keep going until something explodes (been there, done that... ), or I can't find the part that I need (gets to be a real problem with some older Macs. Try to find plastics for early iMacs... That takes some luck, as money often doesn't get you anything - but that's another story for another time.)
 
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lovecd

macrumors regular
Original poster
Aug 14, 2022
164
14
It's possible. On other Macs, I have seen video problems because of a problem in the PSU (perhaps not enough power available to turn on video)
But, as you have fans working, and no chime, you have some power, and you said that you tried a different PSU, and swapped in a different logic board. You have a major component left, which would be the video card.
You have a lot of effort (and some money) in an older iMac, and, at some point, you get to decide if more time and money is worth the result.
You have seen a couple of posts offering the opinion that a 12-year-old iMac is not worth much, so you shouldn't waste your money. I tend to disagree with that viewpoint, as I am a stubborn enough to keep going until something explodes (been there, done that... ), or I can't find the part that I need (gets to be a real problem with some older Macs. Try to find plastics for early iMacs... That takes some luck, as money often doesn't get you anything - but that's another story for another time.)
It is true that it’s not worth the time and money for fixing the old gadget like this, but I’m also a stubborn guy and always exciting of the “achievements” if I can get something working again…, anyway, thank you so much for your advise and will sure to keep you posted.
 
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wolf1734

macrumors regular
Nov 9, 2014
147
17
France
hello I have a similar problem on a 27" iMac from 2009 the screen lights up a little after the start-up bong and stays like that. the inventory has been changed and still the same; the screen has been tested on a another iMac and it Works? the iMac works on an external screen but not with its screen, what can this be?
how to do?
 
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