A500 MegAChip Help

[arongooch]

Hi everyone,

Just finished moving my working MegAChip from my A2000 to my A500. My A500 is a vanilla A500, Rev 5 board with 512KB Chip and 512KB Fast. I cut the JP2 linkage and soldered the bridge towards the top direction of the machine and cut the trace running along the CNX memory connector as shown in the manual. All works good and I see 2MB Chip RAM now.

My question is, why can't some of the memory either the onboard 512KB or the 512KB in the memory expansion connector be used as memory to top up the Fast RAM? I now get 2MB Chip RAM but absolutely NO Fast RAM at all. Is there a hack or something to use some of this RAM as Fast? Before the modification I had 512KB Fast RAM and it was working correctly.

Another question is, does having no Fast RAM in an A500 affect anything in terms of games not working etc? If I left it with just the 2MB Chip and not having any Fast RAM, would I ever get games refusing to work or other problems down the track? Are there known games that refuse to run if an Amiga has no Fast RAM?

Any information would be greatly appreciated. Cheers

[giZmo350]

Hi arongooch, I went through this exact scenario for a few years with my rev 6a m/b. Assuming you have a 512K trap door expansion as I do, I bought a megachip and configured the m/b for 2m/b chip. After thinking maybe I should have configured for 1.5m/b chip and 512k fast (due to no fast ram after mod) I simply never went back to do that as it would have been a pita. So, with that said, I just used it for a few years with 2m/b chip only and never ran across a game or any software for that matter that didn’t work with just 2m/b chip ram.

However, It always bugged me that I had no fast ram when using an HDD with AmigaOS, i.e. A590. Then I ran across this 8m/b fast ram expansion and it works great! 2meg chip plus 8meg fast. These are usually limited in production though. He still has 2 left.

https://www.ebay.com/itm/Commodore-Amiga-CDTV-A500-8MB-RAM-Board/323447083263

It just barely fits under the keyboard so make sure your kb has that plastic film on the bottom or insulate where the ram board just touches the kb.

Also, if you have an Indie ECS scan doubler you’ll have to raise it up to fit above the ram board. No problem with using some of those breakable pin risers. All kinds of room back there. I put two rows under my Indie.

The 8m/b little board is also NOT compatible with any addition fast ram a CPU accelerator provides. I know, I just tried it the other day with one of these HC533 Turbo cards.

https://sordan.ie/product/583/turbo-card-hc533-33mhz-8mb-ram-ide-amiga-500/

I guess I should mention, you can also get 8 meg fast ram with this CPU accelerator.

Good job getting 2m/b chip with your rev 5 m/b. I always heard rev 5’s were troublesome. Anyhoo, hope this helps.

[Oldsmobile_Mike]

I would stick with your current setup: 512K chip on the motherboard, 512K chip on the "A501" trapdoor, and 1MB chip on the MegAChip = 2MB of chip, the max you can have on an Amiga.

Add yourself some fast ram through some other method, such as the side expansion connector or underneath the CPU.  There's many options available, including RAM through a GVP or C= hard drive controller mounted on the side, etc., etc.  Have a look on ebay.  This will give you the best performance (since fast ram added through the side expansion connector or under the CPU will actually give you a performance boost, as opposed to the "fake" fast RAM added through trapdoor).  Good luck!

[arongooch]

Cheers and many thanks for the feedback

I'm planning on returning this A500 back to original configuration to have a machine that is reminiscent of what I had in the early 90's mainly for nostalgic reasons. I have many other Amiga's much more souped up than this machine but was more curious seeing the MegAChip in action in the old A500. If I was to keep the MegAChip in this machine I was thinking the option of additional Fast RAM upgrades as mentioned.

I am still unsure as to why the original 512KB that was Fast RAM could not continue to exist as 512KB Fast with the MegAChip installed. Even with 2MB Chip I would have thought the Amiga could still access up to 8MB Fast as this is addressed by the CPU not the custom chips. Thus I was expecting 2MB Chip and 512KB Fast.

Also what is interesting is that with the MegAChip installed and having its own 2MB Chip RAM onboard and obviously not using the onboard A500 or expansion connector RAM, I find the motherboard 512KB RAM still warming up considerably but the expansion card RAM IC's stay fairly cool. More so than I would have expected considering they are just sitting there doing nothing. Im guessing these old RAM chips are still drawing current and are going to warm up whether used or not but did find it interesting non the less. Perhaps also differences in brands of RAM chips between the onboard A500 and expansion card.

[magnetic]

Dont look for problems if the amiga is operating well. Are they "warm" or "hot" its probably perfectly normal but i havent messed with an a500 in years.

[zipper]

If you have full 2 MB Chip RAM the Megachip delivers 1 MB, rest comes from mobo + exp.slot RAM .

[Oldsmobile_Mike]

Also what is interesting is that with the MegAChip installed and having its own 2MB Chip RAM onboard

As others have already stated, MegaChip has 1MB on board.  The remainder of the 2MB comes from your trapdoor slot and the motherboard.

[arongooch]

Ah, that's it. That's the bit I wasn't understanding. The MegAChip has 1MB on board and the other 1MB is the combination of the A500 onboard & expansion memory.

Was wondering why the onboard RAM was warming up. And no, not getting super hot but more just normal operating temperature.

All makes perfect sense now. Thanks.