A500 w/ FastRAM & IDE: how to get 1MB Chip RAM for WHDLoad games?

[lizageza]

Hi all,


I’ve got an A500 Rev. 5 board with a FAT Agnus and the following setup:

• 8MB Fast RAM
• Internal IDE with CF/SD adapter
• Dual Kickstart ROMs
• SD card with pre-installed OS and WHDLoad

Everything is working fine, and I love the setup — but there’s one recurring problem:


Many WHDLoad games require 1MB of Chip RAM, and my system only has 512K.
I often run into cases where games that used to launch now fail with “Not enough Chip RAM” errors.


I’m wondering:

• Is there a practical way to upgrade to 1MB Chip RAM on this Rev. 5 board with FAT Agnus?
• Would this require a board mod, or could it be done via a trapdoor expansion?
• Are there clean solutions that avoid major internal work?

I’d love to keep this setup as-is (it’s neat and stable), but if there’s a viable path to getting more Chip RAM for WHDLoad, I’d definitely consider it.


Any tips or suggestions from those who’ve done this upgrade would be greatly appreciated!


Thanks,
Géza

 

[bdb]

While I generally configure the 1 MB 8372a Agnus for NTSC, the Agnus will switch in both software and hardware to PAL, and the extra 512K of Chip RAM comes from a trapdoor expansion.

The 8372A supports both PAL and NTSC modes via a “pin 41” selection, unlike the earlier OCS Agnus variants, which are fixed to either PAL (8371) or NTSC (8370).

You need to alter the JP2 jumper to add in the RAM. The JP2 Jumper Location is between the CPU and ROM chip, marked on the PCB.

The stock JP2 should have a solder trace connects the bottom pad and middle pad. You will need to cut this trace (i.e., between the bottom pad and middle pad) using a sharp hobby knife or similar (use the continuity test of a multimeter to check). Next solder a bridge (small drop of solder or a wire – or to be super cool, solder a Zero “0” Ohm resistor) between the middle pad and top pad, leaving no connection to the bottom pad. Optionally, you could put a switch here for those games that don’t like 1 MB of Chip RAM.

I no longer work with A500's so you should check my recommendations against real Amiga Users...