article from Dave's Amiga Hardware Page
The A2000 was originally designed to provide a maximum of 1MB of Chip RAM. Normally expansion to 2MB requires the addition of some kind of plug in module which is hard to find these days. For those with a Rev 6 motherboard, it is possible to upgrade to 2MB by means of a simple hack as shown below.
How to do it
You will require good soldering skills to perform this modification. You will also require 4 x 44C1000 RAM chips, an 8372B Agnus chip, a 33 ohm resistor and a 470 ohm resistor. Note that I originally performed this modification nearly 20 years ago and never documented it at the time. Hopefully I haven't missed anything when documenting it now.
- Remove all 8 existing RAM chips from the motherboard.
- Fit sockets to the 4 upper RAM positions only.
- Remove both R110 and R212.
- Add a wire link from the left terminal of R212 (as viewed from the bottom surface of the motherboard) to pin 36 of the Gary chip. See picture below.
- Add a wire link to pin 5 of the four RAM chips in the top row, connecting them together.
- Add a 33 ohm resistor from pin 5 of the upper RAM chips to pin 4 of U507 (this is one of the bottom row of RAM chips, now removed)
- Add a 470 ohm resistor from pin 5 of the upper RAM chips to +5V. A convenient place for this is pin 1 of RP503.
- Install 4 x 44C1000 RAM chips into the top row sockets.
- Replace the existing Agnus chip with an 8372B (2MB) Agnus.
- Replace the existing Denise chip with a 8373 'Super' Denise, if you wish to upgrade your A2000 to the ECS chipset.
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How the A2000 motherboard looks from the bottom with the mods applied
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| How the A2000 motherboard looks from the top with the mod applied. Hard to tell it's been hacked |
Would a Agnus 318069-11 work?
ReplyDeleteI would like to know too, the 8372B Agnus chip is a pretty rare thing now.
ReplyDelete