Voltage regulator in iMac 27" - screen blackout.
1. Is there a voltage regulator in this iMac? If so, where and how it can be tested for damage, if not that what is the next thing to look at?
2. Can it be replaced?
Long story short:
(Chime normal at startup)
- I did not open the iMac - Apple did. They cannot reproduce the blackout.
- Fans were dusty - Apple blew the dust off (when the iMac was there first time)
- Second time - They "thought" it was the video card and replaced it but came to the conclusion is not that but my upgraded RAM
- It now has the very original RAM - blackout persists!
- It seems like it is having personality fits: today it worked, (just blacked out as I'm writing this), yesterday it did work (even hot) but 2 days ago screen was going in blackout every 2 seconds
- It reacts to Shift-Ctrl-Eject, but not always stays on
- My voltage is going up - from 123.5 (earlier) to 124.9 (as is just blacked out)
- I have a secondary screen attached - so I can finish my work in case blackout happens (as it did)
So, the only variable is the voltage.
Can you help? Please!
My external monitor - Thunderbolt connection to HDMI cable
- I turn on my iMac but the external monitor turns on when I see the password screen
- It will not run on If I try to run diagnostic - (D task)
- it will respond to "Sleep" command"either Shift-Ctrl-Eject or my screen shortcut
- when the iMac screen blackout, the external monitor does not react
So, back to my original question - is there a voltage regulator in this iMac?
Update - Kind of (09/14/2017)
Last advice from Apple Store was that the memory was bad. I returned the original memory in it in order to take it back to the store, but I was busy for about 2 weeks. Now, it seems like the issue is gone. Or, at least it did not happened in the last 3 days.
The voltage fluctuations does not seem to matter like I previously thought. So, the possibility of LED driver board to be bad is slim now.
I still have no explanation why it did not happen at Apple Store (while having the upgraded memory installed).
I assume the fault is with the memory slots (I guess that can be an issue too) and then is not worth to be repaired. The price is half of the computer when was new.
Anybody any ideas on this?
The pic of modules
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