1Mb of Motherboard Memory on the Rev 5  

It is possible to install 1Mb of RAM onto the revision 5 motherboard . However , this modification is flaky at best and I cannot recommend it  (having tried it in a moment of sheer boredom ). Also note that I could  * not *  get this extra memory to be mapped at  $ C00000  ( the computer would only recognise it if I had JP2 set to map the A501 at  $ 80000 );  which means that it is only of potential  interest to owners of the 1MB Agnus . This failure to work as  $ C0 RAM may well  have been due to some stupid omission on my part ).  
        
I will deliberately be vague because this is not a trivial modification .  If  you are unable to work out what to do with confidence ,  you do not have enough  knowledge to perform the mod. The procedure can be summarized as follows :  Take sixteen 41256 RAM chips  ( for  speed information,  see the end of subsection vi .  above ).  Bend the refresh  address strobe pins (RAS,  pin 4 )  on all the chips up and over so that it is  well clear of the other pins and easily accessible from the top of the chip .  Bend in all the other pins a little .  Now ,  piggyback the new chips on top   of the existing RAM ,  making sure to install them in the same orientation as  the original chips .  It is not possible to reach all the pins to solder them ,   so you will have to content yourself with only soldering the corner pins .  

Solder wires from the bent - up RAS pins to pin  # 38 of the A501 port  ( or any  convenient take - off point of this signal ).  You should now have 1Mb of RAM .   ( If  you want to try using it as  $ C00000 RAM ,  you should ground the EXRAM pin ,  pin   # 32 ,  of the A501 port .  I had no success with this ).  This mod sounds all very  well ,  but in the current climate it may be slightly cheaper to buy a  secondhand A501 than to buy 41256 chips .  In addition ,  due to the precarious  hold the piggybacked chips have on the originals  ( because there isn ' t enough  room to solder all of the pins down ),  the mod is sensitive to shock ;  if you  tap the table ,  you can sometimes guru the machine .  For this reason ,  this is a possible but ill -  advised "  modification.