i just put some replacement chips from my old a500 to another board ..including the gary chip an the 2 meg fat agnus ..at first it didnt work ..then i realized that the agnus chip on the other a500 was orientated differently to my original board ..is this common?? ..i thought a a500 board would be the same an chips same as each other ..
I wouldn't expect an a500 board to have a 2meg agnus at all, if it was really a 2meg agnus then it sounds like an a500+ board. Unless someone fitted a 2meg agnus later. However even then the a500 board can't provide 2mb of chip ram, you need an a500+ board. Some people think the ram is inside the agnus, but it's not. The only difference between them is a different number of address lines so they can access more/less memory. Up to rev 5 you could only have 0.5mb on the motherboard, rev 6 added the ability for 1mb on the motherboard but I don't believe any machines shipped like that. If you only had 0.5mb on the motherboard then you need to add 0.5mb trapdoor memory to get 1mb chip ram. Rev 8 was the first to ship with 1mb on the motherboard and support 1mb in the trapdoor. Megachip allows you to have 2mb but that is bypassing the motherboard limitations by using another pcb.
Are you sure it was a 2mb agnus? An 8375 may either be 1mb or 2mb as commodore re-used the same number.
http://en.wikipedia.org/wiki/MOS_Technology_Agnus There were multiple revisions of the mother board, rev 6 or earlier is a500 and 8 is a500+.
