2MB Chip RAM for the A2000.
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.
1: Remove all 8 existing RAM chips from the motherboard.
2: Fit sockets to the 4 upper RAM positions only.
3: Remove both R110 and R212.
4: 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.
5: Add a wire link to pin 5 of the four RAM chips in the top row, connecting them together.
6: 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)
7: 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.
8: Install 4 x 44C1000 RAM chips into the top row sockets.
9: Replace the existing Agnus chip with an 8372B (2MB) Agnus.
10: Replace the existing Denise chip with a 8373 'Super' Denise, if you wish to upgrade your A2000 to the ECS chipset.
Below is how the A2000 motherboard looks from the bottom with the mods applied.
Below is how the A2000 motherboard looks from the top with the mod applied. Hard to tell it's been hacked.
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Introduced 29th April 2015. Last updated 2nd August 2015. Version 1.1