Jonas has Amiga modding questions. Do you have answers?

Intrepid Amigos listener Jonas Rullo recently wrote in with the following:

“Other than a 512MB trapdoor upgrade, is it possible to get over 1MB on a stock 500? I saw some scattered info on changing the Agnus chip but it looks like 2MB is the max and possibly only for the 500+. Also, would you just swap out the Agnus? Do you know of a card that has a place for 2MB of memory in the first place? So far, I’ve only found the 512MB cards for the the 500.

Do you know of a good tutorial on what ECS chips you can directly use in the stock 500? How much of that is possible without daughter boards? I built a ROM switcher when I had my original 500 and I just ordered a 500. If it works as advertised I’ll probably build another switcher since 1.3 is stock.

I’d love to get some links to A500 mods or see an article on your site about whats possible with A500 mods.

I’m excited to get back into real Amiga hardware.

Do you know of any replacement keyboards that could be mapped to an Amiga? I was thinking of getting a 1200 motherboard and building a system in an acrylic case. It seems like building from parts and components is cheaper than paying over $500 with shipping for what’s available on eBay.”

Can anyone help a fellow Amigan out?

8 thoughts on “Jonas has Amiga modding questions. Do you have answers?

  • October 29, 2016 at 11:13 pm

    My understanding from back in the day is maximum 512Kb Chip RAM unless you replaced Agnus which would allow 1Mb Chip RAM internally. Maximum 8Mb Fast RAM externally using side expansion port. The A500+ can take up to 2Mb Chip RAM standard and 8Mb Fast RAM externally. I'm not sure if there are modern upgrades that will allow more.

  • November 3, 2016 at 3:40 am

    Thanks. I'm not really clear on what counts as external or chip RAM. When you add 512K through the trapdoor on the regular A500, does that add to chip RAM or external RAM? Do I need to upgrade Agnus to get the trapdoor RAM to add to chip RAM?

  • November 3, 2016 at 2:46 pm

    Where to start.
    In the old days there were a few ways to add RAM to a 500 to get it up over 1MB. First and most often was to add it on the side expansion port. Like with the 1000, you would buy a box that plugged in there usually with 2MB. Sometimes these boards come up on ebay but are getting rarer and more expensive. This is a popular one:
    due to its relatively small size
    Another popular add on in the old days was to add a third party expansion to the underbelly RAM area which had more than 512k. These boards required a wire, or board be connected on the motherboard to let the Amiga communicate with the RAM on the board over 512K and was non standard but meant you didnt have to connect a box on the side keeping the Amiga portable and small.
    Expansion Systems Baseboard added more RAM in the underbelly slot of the 500 than Commodores
    There even was a PC board for the 500 that served as a 512k RAM expansion when the PC was not in use. It was called the Power PC board.
    Last of the old means of adding RAM was a board called the Insider. this consisted of a board that plugged into the CPU socket on the 500 then you would place the 68000 on the memory board.
    This had 1.5MB bringing the 500 to 2MB internally.

    Modern boards for expanding a 500 over 1MB are the board Kipper2k sells.
    This board can give your 500 4 or 8MB of RAM and a hard drive using a CF Flash card and does require soldering two leads to the motherboard.
    Of course, lastly is the upcoming VampireII which will add RAM and CPU accelerator to the 500. There is currently a version out for the 600 so you can read up on all the features.

    Advantage to the Kipper2k board and the Vampire is they are modern and probably will end up costing as much as the old boards which are going on 20 years old plus. I haven't bought any of the new boards since i have a lot of the old ones.

    Hope all that helps.

  • November 4, 2016 at 5:45 am

    Now on to chips you can upgrade in a 500.
    Agnus is the chip we always wanted to upgrade. That is the one that dictates what Chip RAM you have. The 500 was designed for 1MB Chip Mem, though. So even though with the release of the 3000 and 600 there was a new Super Agnus that could access 2MB, the 500 Motherboard only has the hardware to connect 1MB up to the Agnus chip. This is why companies like DKB came out with boards that go into the Agnus socket (in the move from 1000 to 500 Agnus went from a rectangular DIP package to square PLCC) which have 1MB on the board and the socket for the Super Agnus on top. Other than that, the only reason you might upgrade an Agnus on a 500 is if the machine only sees 512K even with a 501 RAM board or equivalent in the trapdoor expansion under the machine. This is because early 500s came out before the new Agnus was ready. So though the motherboard was setup for 1MB, and the socket ready to accept the Fat Agnus, they had to place the older 512k Agnus in the machine to get it out the door for sale. So if your 500 has an 8370 for NTSC or 8371 for PAL Agnus you can replace it with one that supports 1MB. This is a bit complicated with some crazy numberings from Commodore.
    This page has a great list of the Agnus chips and what they support both RAM and video standard:
    Paula is an easy chip. That one was not changed from the DIP format and no changes were made to its capabilities from the 1000 all the way up to the 3000 and all machines in between. Though it did change to a surface mount chip in later machines.
    Denise is easier than Agnus since there is no RAM access component. But you can gain some features using a later Denise chip. Denise is a chip that like Paula did not change from a rectangular DIP package even with the change from OCS to ECS chipset. So if your 500 has an 8362 R6 Denise (OCS) you can replace it with an 8373 R4 Super Denise. This chip adds extra half bright color modes (up to 64 colors on screen by taking the 32 colors and adding 32 at half their brightness) and can also add some additional high res screenmodes. So it is a worthy replacement if you can find one.

    Creating a 1200 from parts is quite possible. The heart of the machine is the motherboard. Floppy is a standard Amiga floppy, and the power supply is a standard Amiga 500 though i believe the 500 is actually a better supply since it was built assuming it might have to power devices on the left side expansion as well. So as you surmise the only question is a keyboard. Getting a 1200 keyboard can be expensive nowadays but the trend by some to want to towerize the 1200 made some manufacturers release boards that brought the keyboard to the back where a plug in keyboard could be added.
    There is the DCE Keyboard Interface that, I believe, would let you use a 2000, 3000 keyboard (or 4000 with a suitable adapter)
    The Elbox PC-Key 1200 let you use standard PC AT style keyboards (and I assume PS/2 with an adapter)
    Indavidual Computers Lyra 1200 lets you use PS/2 keyboards.
    The DCE clips on top of a CIA chip. PC-Key 1200 goes in the keyboard connector slot and the Lyra 1200 clips on the MPU. All three then have a wire to the external keyboard port on a backplane for attaching to the back of a tower case.

    Guru Anthony

  • November 8, 2016 at 6:54 am

    Only the very earliest 500s came with Agnus chips that could not access the trapdoor 512k as Chip RAM. In those systems, the trapdoor RAM comes up as 'Slow RAM". Not quite fast, not quite chip. In those systems you would need to replace the Agnus chip. I have the chip numbers in my reply below.
    Most 500s you don'd have to update the Agnus since the new chip was out pretty early and every 500 after that came with the 1MB Agnus chip.

  • November 8, 2016 at 6:57 am

    Trapdoor is Chip RAM (unless the Agnus is too old in which case it has to be replaced with the newer one). In most 500s you wont have to upgrade Agnus.
    You can either place the trapdoor RAM card in and see what you get, or open the machine. If the Agnus chip is an 8370 or 8371 it will have to be replaced to get 1MB Chip RAM.

  • November 13, 2016 at 7:34 am

    On the oldschool AMIGA the maximum upgrade is 42MB RAM on one of those normally.

    Up to 2MB like the A600 setup regualar internal RAM could be fitted.

    Up to 32MB could be fitted in a cheaper oldschool accelerator making it 34MB total with the 2MB internal combo.

    Up to 8MB on a side expansion giving you your most powerhouse setting of 42MB.

    Now heres the big but. You can now go modern on the accelorator with the rarity of the Vampire A500 V2.

    If you are lucky enough to grab one when they are back up on the ebay account they can hold 128MB so 138MB would be what you would get on the same config of the 2MB internal, 8MB side and 128MB processor upgrade the fastest the A500 now can get is that I guess but the Vampire A500 is always out of stock I've never seen one actually sold although in his ebay feedback clearly some had been sold in the past.

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