I have 512k external memory expansion board. After the soldering, it is possible to have of total 1.5Mb ram?
No. While it is possible to use Agnus to expand beyond 1 MB (I'm assuming an A500 non-Plus here), you'd have to provide for some address decoding. The easiest way would be to get hold of one of these 2 MB boards - if you're using 1 MB as chipram, you'd have to make sure that the expansion board supports that setup.
