My experience with sending machines to Bitmain for (under warranty) repair has been very commendable.
Unfortunately, I have had to send in 4 machines up to this point. Also, I am not sending them to China. If you are in the US, you send
them to LA. They test the machine the day they receive it, confirm that it does indeed have a problem. They process it w/ China and I usually
receive a repaired machine within 3 business days. It does kinda irk me that I send in a new machine for repair and usually receive a clearly used sometimes
dirty, visible ware on the outside, machine back. However, as long as it works, I can live with that. Does Bitmain repair machines that are out of warranty?

Bitmain Warranty is a different story......

6 weeks ago I sent in 3 hashing boards for a S7. I never got notified that they received until I emailed them 2 weeks later. I have never got any kinda update about my
boards whether they have been looked at/repair/repairable/paperweights/etc. I emailed them last Friday. They responded that they have not been able to repair them
and that this week they were gonna give it another try. You can never get them on the phone, the experience just kinda makes me think that they get there stock from
people that send stuff to them and "they can't repair it", then stock shows up on their website for sale. Maybe not. Maybe they will actually email me back sometime. And if
they are unrepairable they will actually mail them back to me, only time will tell.

Anyway, that is my experience with the 2 repair services.

Now I'm gonna go do a Block dance out in the garage. I hope it helps.