After an hour of struggling with the shorts I decided to put back the original ROM. Lo and behold, the PS1 is alive again: boots properly, starts game CDs. (only one pad was torn during removing my custom PCB...)
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Thanks for the reply and sorry for not being too active lately.

This is what I did yesterday:
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In the middle of the ...

Okay,
first, I somehow mixed things up and write BIOS ROM chip instead of BOOT ROM chip. I meant BOOT ROM chip in the original post.
Secondly, I replaced the 220uF caps, no change on the half-booting PS1
Thirdly, I found a blown fuse in the blackscreen PS1 (it was on the 3.3V line), replaced, that ...

Hi,
I got two faulty consoles recently, none of them boots properly (one shows a simple black screen, the other one shows the first boot screen, but with garbled sound/noise and doesn't proceed from there).
I watched a ton of YT videos and read a few articles and I came to the conclusion that this ...