This is an old post, preserved for reference.
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The classic rubber keyed Sinclair ZX Spectrum came in many versions. This one is issue 2, the first one produced in any volume.
DivMMC Future board, which I have been tweaking the design of to make it work with all the different versions of the Spectrum.
zx.zigg.net). That confirmed the lower 16K RAM was fine, but there was a fault (or rather several faults) in the upper 32K RAM.
DivMMC future, it did that automatically, no dip switches or jumpers, only the menu and reset buttons.
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2022 Update: The production version of the DivMMC future is now available from The Future Was 8 bit