Looping chime on booting 2010 i7 iMac 27

[Daud]

On start, it sounds the start-up chime repeatedly looping in 3 sec distance. Fans spin up, Superdrive is trying to read the DVD stuck there incidentally when iMac crashed. System is modified with HD replaced with SSD and SATA-to-eSATA cable looped through the bottom out. System worked after modification in 2017 for almost 2 years.
Tried:
- memory reseating, moving around
-checked the LEDs on motherboard, with screen off, first 3 are on (the last one would indicate intact (??) video card?)
- all standard wired keyboard tricks Command-Option-P-R keys, Shift+Control+Option keys with Power, (but keyboard/USB might not be working, i.e.Eject and left mouse click on start do not kick the DVD out)
-replaced the SSD with the original Apple HD
-I got nowhere with the attempt for diagnostics (D) or target mode (T).

The screen remains black, iMac trying to start up in a loop.

My suspicion is I got the video card failure just by probability.

Shall I get a cheap 2010 video card, I think the one from i3 should be compatible (Radeon HD 5670 512MB) and as a trial, replace the video card if this helps ? Or explant my card and bake it ? Is there a way for locating the problem?
I think I can't do much more on my end and don't want to spend too much on shop diagnostic fee (<$100?).

 

[Fishrrman]

A replacement video card might work, but then again, if you spend the $$ to put one in and it DOESN'T work, you're just out that much more $$$.

After 10 years, might be time to start looking around for a replacement, either new or perhaps Apple refurbished. If iMacs are too much $$$, consider a 2018/2020 Mini -- they're dandy little Macs.

 

[Daud]

As it is $$ not $$$ I will possibly try this last option. I can still sell the card for $-$$

 

[Daud]

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 for the 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 here about 2011 iMac upgrade) but it might be above my skills with flashing the new card and manipulating the system.

 

[USB3foriMac]

Glad and happy to hear another piece of hardware was saved from the bins and will continue to be in service.
If you don't NEED MacOS, try a Live Linux Mint 20, or install Windows 10 (and get a valid and totally legal key for as low as $4). In that case you will have latest up-to-date OS at (almost) no extra charge.

 

[Ausdauersportler]

Had this after replacing a dead GPU in a mid 2011 with a good one - take a look at my signature. Had to disassemble an reassemble the complete iMac to solve this.

PRAM reset was not possible and SMC reset did not work.

Now the system is running BiG Sur public beta 2 with an Nvidia K4100 installed. Everything is possible