Hi. thanks for your answer.
My system is pi 4 with 8gb ram with pre-build iso version 7.1.1 reloaded of recalbox.
Roms and bios are on a 3.1 usb-stick with 128 gb.
In the bios-checker every psx bios appears green with thumb up. Md5 check is also good.
But if i start a psx rom. It always appears a message, that no bios file is found.
I also tried different sources for the psx-bios files. But the problem stays the same. Most psx isos crash after a while with one emulator, with the other just a white screen apears with text, that scph5501.bin file is missing
But in the bios checker, it seems to be good.
I have no clue what the problem could be.