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Thread: 2megs ChipRAM on rev.6a Amiga 500 Motherboard

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    Metalguy66's Avatar
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    Default 2megs ChipRAM on rev.6a Amiga 500 Motherboard

    A while back, a guy named Wild Cobra on Amiga.org brought the following to my attention: As evidenced by the service manual schematics, with the right jumper settings, the rev 6a Amiga 500 is actually designed to accept an A3000 Agnus chip and a full 2 megs of ChipRAM on the motherboard!

    This does require DRAM of a higher density (1meg x 4) than stock, but the additional address lines are already present on the motherboard both on the DRAM side as well as the CPU side of Agnus.

    All that has to be done is to replace the Agnus chip with the A3000 part, remove the factory 256k x 4 DRAM chips, install four 1meg x 4 DRAM chips, and make the appropriate jumper changes to enable it.

    Recently, I was able to verify that this does in fact work on real physical hardware in front of me. All of the "docs" I've seen on Aminet and elsewhere in the past have seemed to reflect that you need to build a quite involved hardware project in order to accomplish this. They are wrong.

    So, for the benefit of all who may wish to have these instructions, please have a look at this:



    note: Only an actual A3000 Agnus (one of the two part numbers listed in the diagram) will work. 2meg Agnus chips made for the A500+ or A600 will not work as they have a vastly different pin arrangement. I have done my absolute best to include all needed instructions/details in this single .jpg image. Enjoy.

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    DesktopDynamite's Avatar
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    Quote Originally Posted by Metalguy66 View Post
    A while back, a guy named Wild Cobra on Amiga.org brought the following to my attention: As evidenced by the service manual schematics, with the right jumper settings, the rev 6a Amiga 500 is actually designed to accept an A3000 Agnus chip and a full 2 megs of ChipRAM on the motherboard!

    This does require DRAM of a higher density (1meg x 4) than stock, but the additional address lines are already present on the motherboard both on the DRAM side as well as the CPU side of Agnus.

    All that has to be done is to replace the Agnus chip with the A3000 part, remove the factory 256k x 4 DRAM chips, install four 1meg x 4 DRAM chips, and make the appropriate jumper changes to enable it.

    Recently, I was able to verify that this does in fact work on real physical hardware in front of me. All of the "docs" I've seen on Aminet and elsewhere in the past have seemed to reflect that you need to build a quite involved hardware project in order to accomplish this. They are wrong.

    So, for the benefit of all who may wish to have these instructions, please have a look at this:



    note: Only an actual A3000 Agnus (one of the two part numbers listed in the diagram) will work. 2meg Agnus chips made for the A500+ or A600 will not work as they have a vastly different pin arrangement. I have done my absolute best to include all needed instructions/details in this single .jpg image. Enjoy.
    Thanks for this info. So if you do not find required Ram chips to be soldered, say a rev 5 to achieve 2Mb chipmem, one can still acquire a DKB megachip or mini megi still right?
    Correct me if I am wrong..
    1x Amiga 500
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    Metalguy66's Avatar
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    This has nothing to do with a rev. 5. Yes there are many rare/expensive adaptor boards out there that can be used to upgrade other machines and versions.

    The DRAM shouldn't be too hard to find. Do a Google search for 514400 DIP.

    I would guess that it would be much harder to source an A3000 Agnus chip, but ask around in the normal Amiga hardware channels and I'm sure someone has one they would part with for a reasonable price.

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    Amibayer! DonutKing's Avatar
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    This is great news! Now to track down the right agnus...

    Are we limited to the two part numbers on the image, or would other models of Agnus work?
    Last edited by DonutKing; 19th October 2016 at 22:11.

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    Metalguy66's Avatar
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    ***ONLY THE TWO PART NUMBERS LISTED IN THE DIAGRAM WORK***
    These are the two specific Agnus models used in the A3000.

    The other variations of the 8375 and 8372B are either not 2meg models, or have a vastly different pin arrangement and will not work. Agnus chips designed for the A600 or A500+ will NOT work.
    Last edited by Metalguy66; 20th October 2016 at 00:30.

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    Well, it looks like my next Amiga project.
    Thanks for shared info!
    V2 Vampirized A500 Rev. 6A;
    One fully working C64 + Xpander + 1541 Ultimate II

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    awesome ! I never thought that 2 MB CHIP can be run on rev 6!

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    Thanks Metalguy, I actually have a spare 8372AB lying around so I've ordered some ram chips and will upgrade my Rev 6a A500 shortly!
    500 w/ KS1.3/3.1, 1Mb Chip-Ram, CF-IDE w/4MB Fast-Ram, FDD Selector, HxC RevC Floppy emulator Amiga 600 w/ KS1.3/3.1, 2Mb Chip-Ram, 1GB CF-HDD 1200 w/ KS3.1, ACA1220 26Mhz 128MB w/ RTC, 4GB CF-HDD, Roland MT-32 MIDI Synthesiser 64 w/ 1541 Ultimate-II + Tape Adapter, JiffyDOS, 1541 Disk Drive, 1531 Datasette, Flyer Net Modem

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    So an 8375 works? I thought that they were quite a bit different electrically pinout wise than the 8372B.

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    Quote Originally Posted by cowdog360 View Post
    So an 8375 works? I thought that they were quite a bit different electrically pinout wise than the 8372B.
    Yeah my thoughts too, the pin out is quite different.
    500 w/ KS1.3/3.1, 1Mb Chip-Ram, CF-IDE w/4MB Fast-Ram, FDD Selector, HxC RevC Floppy emulator Amiga 600 w/ KS1.3/3.1, 2Mb Chip-Ram, 1GB CF-HDD 1200 w/ KS3.1, ACA1220 26Mhz 128MB w/ RTC, 4GB CF-HDD, Roland MT-32 MIDI Synthesiser 64 w/ 1541 Ultimate-II + Tape Adapter, JiffyDOS, 1541 Disk Drive, 1531 Datasette, Flyer Net Modem

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