I have an Amiga 500 revision 6A, with a green boot screen.
I suspected Fat Agnus, so I replace it. After the swap I started ATK (Amiga Test Kit) but it didn’t detect any memory at all.
DIAGROM did detected 256KB Chip RAM, but failed to test it after 256KB RAM. I measured all the memory chips address lines with my scope for data signal, they received data, so that’s ok. So, lets have a look at the Fat Agnus PLCC socket..
Pin 77 is corroded, and that’s is A18, ahhh.. Strange that only that pin is corroded.. but ok..
The pin is very loose, so I put a tool behind it, and started ATK again. 512KB Chip memory detected.
ATK looped memory test for 423 rounds without problems, so that socket is the problem and needs to be replaced.