The +2A shares the same motherboard as the +3 (the Z70830).
In theory you can turn one into a +3 by adding all the missing components. +2As are pretty rare though so doing this would ruin it really :-)
If you have a +2B motherboard (much much more likely) then there is no provision for adding the missing floppy disk controller gubbins on the motherboard.
Amstrad planned to release an external version (The SI-1). This was never actually released, but they put the signals required on the expansion port of both boards, so it is possible to build a "not-technically-a-clone" of the SI-1 for both the +2A or +2B.
Even though mine says +2a on the case, the board looks like the one you describe for the +2b with no space to add the missing components. So eBay it is then!
That circuit is a little odd in that it implements the data separator itself rather than using the obsolete SED9420. Unfortunately it uses a 32 byte BPROM which is also obsolete :p
Since ebay etc have been invented used and new old stock SED9420 are not impossible to get hold of, if I had a +2A/B I would be inclined to build it more like the original circuit.
If there is interest I can draw up what my idea for an SI-1 "clone" would be, based on my research on the oddities in the +3 motherboard.
Comments
In theory you can turn one into a +3 by adding all the missing components. +2As are pretty rare though so doing this would ruin it really :-)
If you have a +2B motherboard (much much more likely) then there is no provision for adding the missing floppy disk controller gubbins on the motherboard.
Amstrad planned to release an external version (The SI-1). This was never actually released, but they put the signals required on the expansion port of both boards, so it is possible to build a "not-technically-a-clone" of the SI-1 for both the +2A or +2B.
-Stacey
http://www.worldofspectrum.org/BackToThePlus3/
Since ebay etc have been invented used and new old stock SED9420 are not impossible to get hold of, if I had a +2A/B I would be inclined to build it more like the original circuit.
If there is interest I can draw up what my idea for an SI-1 "clone" would be, based on my research on the oddities in the +3 motherboard.