Actually, all PLCC Agnus types can control 1 MB RAM. However, the older OCS types cannot make it usable as chipmem due to register restrictions - setting them up that way will crash the system. So C= invented the remapping from $08 to $C0 (J101 on 2-3) to render it useless as chipmem; Gary requires the _EXRAM signal to activate the RAM up there (J500 closed). J101 on 1-2 will map the 2nd 512KB to $08 as chipmem and requires J500 open and a compatible Agnus. (J500 open will NEVER deactivate the RTC, this is definitely nonsense on BBoAH).
J101 on 2-3 will remap the RAM to $C0 for Agnus but J500 open deactivates it with Gary - so only 512 KB visible is what is set up. Move J101 to 1-2 with an ECS Agnus or close J500 with an OCS Agnus. Both J101 on 1-2 and J500 closed will activate the 2nd 512K on BOTH locations - which will crash the system, obviously.
J102 is NTSC (closed) vs PAL (open) with a switchable Agnus. There's no connection to the RAM modes whatsoever.
If the RAM isn't accepted (added to system on boot) I suspect a bad contact or a bad RAM chip in the 2nd bank. Run a RAM tester on absolute addresses $080000 - $FFFFFF.
If you're not sure that it's been working with this exact Agnus at all, it is possible that it's a 2 MB type which won't work in a 2000 that way. You need to check with the exact part no.
