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Thread: 8375 AGNUS for A500 rev6a mod

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    piacc64's Avatar
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    i have modded an a2000 rev 6 with 8372ab and new ram, same mod for a500 rev6

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    Math inside Amibayer! BLTCON0's Avatar
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    Quote Originally Posted by DjCook View Post
    seems You have a lot experience in it.. Respect!
    i have two amigas here, first is a standard A500 rev.6A and other is A500 with rev.8A board, 8375 Agnus, and (initially) 512kb of RAM. I have added TTL logic and 512kb onBoard, modded the jumpers JP2 & JP7A to add expansion to chipRAM, and now i have 1.5Mb, hope will get 1Mb expansion soon and then it will be 2Mb.
    I think Individual Computers now makes a 512 KB expansion with a passthrough connector so you can plug your existing 512 KB card too and have 1 MB on the trapdoor. Might want to consider that option too.


    My question is same as the topicstarter has:
    how can i reach 1.5 - 2Mb on a standard rev.6A board without purchasing expensive MiniMega? propably, the best way is just to lookin for rev.8A board, and do same upgrades i've done on my machine, cause the price for 8375 Agnus (or miniMega) is pretty high, and You'll end up with same price You A500 rev.8 can get!

    With the 8372B etc Agnus (and suitable RAM chips) you can't get 1.5 MBytes, it goes straight to 2 MBytes.
    I will agree, the most practical solution is to get a rev8A board.

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    Jack of Many Trades, Semi-Master of Some thebajaguy's Avatar
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    Search Metalguy66 here on Amibay for the thread and image.

    I have also done the above A500 Rev 6a mod to 2MB Chip RAM. You need the A3000's 8372AB or B (the B is what counts), or the applicable (and rare) A3000-replacement 8375 Agnus (318069-18PAL/-19NTSC) 2MB Agnus - note that there is a signal that needs to be addressed (just like the A2000 Rev 6.4/6.5 mod for the -16/-17 chips) on the latter 8375 variant (hence the VBB marking). They both have the classic pin out for the A3000. The A500's existing 4 256x4 RAM chips are removed. You need the VERY low profile machine pins sockets if you are going to use sockets, and put them in the RAM places next to the chips you removed. The 1MbitX4 (4 pieces) memory is very hard to find in DIP - it took me a few tries - but they go in the sockets. The J2 (3-pin, switch positions)/JP7A (all 3 spots open) changes for typical 1MB Chip RAM are done, plus JP3 goes from 2x horizontal traces (=) to 2x vertical(||) solder blobs, and the JP5 setting, which at the top has a reverse L - that L gets cut completely (2 cuts), and what was the top of the L, solder that to the pad to the left. Leave the lower 2=2 pads intact.

    I tracked down someone with made-to-order A500/500+ trapdoor Ram/clock modules, and got just the clock, no RAM, with a SuperCap, though a battery was an option.
    Last edited by thebajaguy; 4th November 2017 at 06:11.
    A500/A1000/A1200/A2000(4x)/A3000D(2x)/A4000D(under repair)/A4000T loaded....Toys...Toys...Toys...
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