I have an APX7k that is dead after I tried "doing things" with communication between CPS and radio. No mercy, it was all my fault

It does not power up and is not recognized on USB anymore, even not in flashzap mode. Now I wonder if there is a way to bootload it with an serial cable, like it can be done for example with TETRA radios.
Any ideas on this?
Thanks a lot for any input!
R.