Okay, am I right here:
You have connected at first a Serial/UART and you somehow messed up something ( Uboot, stage1,..).
and you can't get a console over UART now.
So if you load everything from SATA (Stage1 & Uboot), then you shoud get uboot, stage1 and so UART back to live.
If you cant get UART back to live this way there are not so much things to investigate.
1. Check if you did everything correct with the sata boot disk(Script, right port/bay,..)
2. If boot disk is ok UART is the problem here: Check if every contact still in good shape, if you got an other device with uart check if its working there, check if baudrate and so on is still correct,...
If you didn't find an error: check again as far as I know If you do not physical damage the board, I see no possible way to brick the rescue boot as this is integradet in the SoC
Btw.: Is your kd20 still beeping after power it up?
You have connected at first a Serial/UART and you somehow messed up something ( Uboot, stage1,..).
and you can't get a console over UART now.
So if you load everything from SATA (Stage1 & Uboot), then you shoud get uboot, stage1 and so UART back to live.
If you cant get UART back to live this way there are not so much things to investigate.
1. Check if you did everything correct with the sata boot disk(Script, right port/bay,..)
2. If boot disk is ok UART is the problem here: Check if every contact still in good shape, if you got an other device with uart check if its working there, check if baudrate and so on is still correct,...
If you didn't find an error: check again as far as I know If you do not physical damage the board, I see no possible way to brick the rescue boot as this is integradet in the SoC
Btw.: Is your kd20 still beeping after power it up?