2 
1 Reviving iMac 2010 with looping chime on booting, VIDEOcard was faulty
Around 2017 iMac was upgraded with an Angelfire SSD drive in primary position using OWC NewerTech AdaptaDrive bracket and OWC In-line Digital Thermal Sensor. I used the opportunity to disassemble more to access the SPARE SATA connector and connected a SATA to eSATAcable, pulling it out through the memory door. The iMac was working well for 2 years. It stopped working when wife was using it, abruptly black screen but able to restart once and again several days later but since then, upon restart, it sounds the start-up chime looping in 3 sec distance.
Tried resetting RAM and moving it around, Command-Option-P-R keys, Shift+Control+Option keys with Power, no help. The screen stays black. Ultimately, I have to hold the Power button to force it shut down.
I was looking on ebay, realized sale prices are around $400, nonworking $150.
Today finally found time to go back to it and explanted the SSD drive which is readable so it not the problem, but rather hardware.
Having the data, shall I just sell it as-is with no security updates for High Sierra after Nov 2020 :-( or take it to a local Apple certified repair shop for diagnostics ? But then I am looking for the dig fee plus repair work plus parts cost.
Is there any more troubleshooting I can do on my side ?
Update (08/22/2020)
EDIT: I corrected the title and some text to be more precise about the sound.
________
Dan,
thank you for the hint. With screen off and starting this time from the original Apple drive I kept on shelf (to rule out the role of the SSD), the problem is still present. The LEDs are up, initially the first 2, with the first sound also the 3rd. I can’t see the 4th through the holes on the bottom but it should not be UP anyway if the screen is off.
Can the GPU still be faulty despite the 3rd LED is ON ?
Reading the web, GPU seems to be an Achilles heel of this iMac. People even upgrade with non-original video cards, flash them and are able to run Catalina, pushing past the High Sierra limit.
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4 件のコメント
Here’s some useful Apple T/N’s:
About Mac startup tones
If your Mac doesn't start up all the way
Dan さんによる
OK, that update was useful!
Using a wired keyboard let's give this a try. Restart your system and press the D key to enter into the systems onboard diagnostics are you able to? If not try the T key that will put the system into Target Disk Mode.
Reference: Mac startup key combinations
Dan さんによる
I reassembled the iMac with the original Apple HD in.
I got nowhere with the attempt for diagnostics (D) or target mode (T).
On top, there is a DVD in the drive I can't eject (Eject or left mouse on startup).
By probability, it is the video card. If I would have a spare one, I would change it.
Or, there are used card around $150 on ebay (possibly baked) or Original HD6970M 2 GB on Aliexpress for $90 (it was in 2011 iMac). But without certainty where is the problem, I might need to pay for the diagnostics.
David Simper さんによる
I purchased the least expensive video card Radeon HD 5670 512MB which was in the i3 version of this 2010 iMac. I followed the instruction here for exchange. Be aware, that the temp sensor for the video card is difficult to remove (pry horizontally to the back of the iMac) and reassemble (be careful not to bend the two golden pins in the socket as you insert the connector again horizontally from back to front).
The computer works again, hooray. Yes, the card is inferior than the the original but it will be enough for the expected use. If it will fail again, I might go the direction of adapting a modern card (see the huge thread on Macrumors about 2011 iMac upgrade) but it might be above my skills with flashing the new card and manipulating the system.
David Simper さんによる