Diagnostics and repairs are performed by an engineer certified by Bitmain.
You should only entrust your miners to people who have received the BItmain certification for your model (here the S19 family of miners).
In this way, you are assured that your antiminer will be diagnosed, repaired and tested according to the recommendations of the manufacturer Bitmain.
Here is our certification, do not hesitate to ask for it if you choose another repair shop.