I'd hope DJI have some decent analysis process to get some idea of it's a gimbal motor, connection cable, board type problem.
I think they would have enough parts on hand to try a gimbal setup, and if the problem is still there, try a cable, then a board, etc.
You'd hope they aren't like motor car dealer service mechanics, just whack a $1000 ecu in, if it's not fixed, another $500 part, etc until it's running normal again. A lot of them do this, leave the new part in, "of course you needed that !".
Mostly though, they will probably ship you a refurb, and repair yours in bulk with a heap of others later, possibly even sending them back to China to be repaired in bulk.
Sadly, that is almost exactluy like it seems like. I shipped the drone dirsctly to the service center in New Jersey from Utah. The shipping was was paid for by them, so no complaints there.
Once they had received it, I received the phone call saying it needed a gimbal and camera to the tune of $438. Since I sent it to the professionals, I said of course, do it.
So, if you ever sent a drone to DJI, you can check the status of the repair at any time. My drone sat in the "repairing your drone" phase for less than 24 hours and then sat in "inspecting your drone" for 4 days after the repair was made. Now, keep in mind that his was over the weekend so I figured they get Saturday and Sunday off work. No problem at all.
Monday I received a call and that is when theytell me they are getting all the errors still and it was going to have to go to DJI corperate to get a thorough examination and repair. I was also assured there was no extra cost for this AND it normally takes less than 14 days to get it back to me. Also, Not a problem at all.
But, Back to your statement, I assumed they would go thru a series of technical tests also to pinpoint the specific problem but this one deemed a little more difficult and not a standard problem. But I'm actually more surprised the Service Center so quickly deemed it beyond their repair paygrade and sent it to the true experts to get fixed so quickly. But yup, it looks like they threw the gimbal and camera on, charged me for it and it did't fix anything. I didn't think fast enough and ask to keep the old one, so it probably ended up in th etrash.
Don't get me wrong, I'm not complaining at all. I knew I bought a drone that needed a repair and that is on me. I'm in no rush to get it back as a necessity (but I wish it was back so I could fly it. haha). I have been assured that the rest of the repairs are free of charge so they are sticking to the initial repair quote, which is awesome. And the communication has been great.
Now, my only concern really is that when I get the drone back, I hope it arrives in the Pelican case I shipped it in originally to ship it safely. I did put a note inside and on the repair request to ship it back in the same case, but we shall see.