2.3 MB RAM on A500 through Trapdoor - help needed

[Zac67]

I guess whiteb was refering to JP2, which maps trapdoor RAM to  C00000 ('Ranger' memory) or 080000 (for 1 MB chip RAM). The JP2 setting has to correspond with the Gary adapter your expansion is using; for an older model you'd probably have to limit chip mem to 512 KB (C0 setting) to be able to use all RAM. The same applies if your Agnus can't handle 1 MB chip (but then the jumper would already be set to C0).

[Zac67]

I was wondering about the JP2 cable, too. But this actually does make sense, as the 'A19' line to the trapdoor board is routed through the gary adapter.
Not necessarily for your board though...