This would suggest:
1. The original 8364 is still defective, sounds as though that part is still fitted?
2. The replacement 8364 is also defective, as ~3.6V measured at the supply pin suggests it's drawing excessive current, and there's no serial data output
3. The CPU, ROM, most of the data/address bus, etc, is likely OK as the serial data out looks sane
1. The original 8364 isn't in the socket anymore as it gave me low voltage on these pins pin 32 (P0X): 0.05V, pin 33 (P0Y): 0.05V, pin 35 (P1X): 0.06V, pin 36 (P1Y): 0.06V. The newly bought Paula is currently in the socket.
2. I cleaned Paula's area with IPA and am getting the 4.67V on the new Paula. Will check voltage on the new Paula's P0-1X and P0-1Y though.
3. You are right, apart from the BADPAULA and weird graphics issue that is probably related to the bus between Denise and Paula, everything else seems to be working fine as I'm getting valid serial output.
I think that the best approach from this point on is that I have to dig in the world of the oscilloscope and learn how to use it properly or get a working A500 Rev6A board and test the ICs from my original board with it. I will definitely look into the oscilloscope and learn as much as I can about it, as it is a powerful tool that will definitely be useful if I encounter more issues further on.
These are definitely the best two approaches I could do now, so I will reach out when I successfully boot into the 1.3's Floppy Screen once again.
Thank you for your help Castellen,
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poroxius, February 2, 2026
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