White Screen After upgrade

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iMac Intel 21.5インチ EMC 2544

モデル番号 A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7プロセッサ

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Morgan Grundy @morgangrundy

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投稿日: 2020年5月18日

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White Screen After upgrade

I recently upgraded my, hard drive to an SSD, RAM to 16GB, and CPU to an i7. The upgrade went well.

The iMac booted up and I installed Mountain Lion. Then upgraded to Catalina. The computer worked great for a week really fast.

Then it got stuck trying to close a program. I waited for about 15 minutes and then when nothing responded I did a hard restart. Now I get only a white screen on boot with the chime. Here is what I have tried:

Restart with D pressed- nothing
Restart into safe mode (shift) - nothing
Reseting the PRAM - Chime and white screen for a second then reboot. Still at white screen.

I have removed the display again to look a the diagnostic LEDs. They look normal. Single when plugged in. Second on boot, third quickly follows and no fourth. I replaced the display and all four LEDs light.

What additional steps can I try?

It seems really odd that it was working for a week with no issues but now won’t boot.

RAM and SSD are from OWC and the CPU was purchased used.

I swapped the other CPU back in but still nothing.

Thanks for any help or suggestions you can provide.

Here are the images of the display connectors.

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Dan @danj

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If the onboard diagnostic LED’s are lit that tells me your display its self has a problem. I would see if an external monitor works, if it does then that proves it.

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That is a good idea Dan. Thanks. I will have to get a mini-display port to HDMI before I can test. Do you know if the iMac will immediately recognize the external monitor? I can't get into the settings to change anything.

Morgan Grundy さんによる2020年5月18日

You should see your desktop.

Dan さんによる2020年5月18日

Hi Dan, I got the cable and tested it. I still only see a white screen (with the boot chime) on the imac. The external display show no signal. Do you have any suggestions for how to troubleshoot? Thanks

Morgan Grundy さんによる2020年5月24日

OK now we have a conflict of diagnostic processes. You stated the onboard LED's #1, #2, & #3 lit and as the display was not connected #4 was not lit.

Now you're telling me the external display is not working. So thats telling me your GPU has failed or your logic board display data cable connector logic has been damaged.

Open the system up carefully disconnect the display again and take some nice clear pics of the connector (tight) and of the logic board around it (a good 3 inches) post them here for me to see iFixitでの質問に画像を追加する方法

Dan さんによる2020年5月24日

Hi Dan, Really appreciate you help with this. I did not understand your original suggestion. I tried the external monitor with the iMac display attached. I just tried plugging in the external monitor without the display. Still just the white screen. The three LEDs light but not the fourth. Would that point to the logic board?

Morgan Grundy さんによる2020年5月26日

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That is a good idea Dan. Thanks. I will have to get a mini-display port to HDMI before I can test. Do you know if the iMac will immediately recognize the external monitor? I can't get into the settings to change anything. — Morgan Grundy
Hi Dan, I got the cable and tested it. I still only see a white screen (with the boot chime) on the imac. The external display show no signal. Do you have any suggestions for how to troubleshoot? Thanks — Morgan Grundy
OK now we have a conflict of diagnostic processes. You stated the onboard LED's #1, #2, & #3 lit and as the display was not connected #4 was not lit.

Now you're telling me the external display is not working. So thats telling me your GPU has failed or your logic board display data cable connector logic has been damaged.

Open the system up carefully disconnect the display again and take some nice clear pics of the connector (tight) and of the logic board around it (a good 3 inches) post them here for me to see iFixitでの質問に画像を追加する方法 — Dan
Hi Dan, Really appreciate you help with this. I did not understand your original suggestion. I tried the external monitor with the iMac display attached. I just tried plugging in the external monitor without the display. Still just the white screen. The three LEDs light but not the fourth. Would that point to the logic board? — Morgan Grundy

iMac Intel 21.5インチ EMC 2544

White Screen After upgrade

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