From: belitz@genesis.informatik.rwth-aachen.de (Matthias Belitz) Subject: 600 XL memory upgrade with two chips Hello !!! Here is how to do it ! All you will need are two dynamic RAM 4464 (64*4 bit) and a piece of cable. First open the computer. Then pull out the old RAMs U11 and U12 (both 4416). Now pull out U5, U6 (Multiplexer , LS 158/157) and U18. Now you have to lift up some pins of these chips so that they won't have any contact to the socket if they are plugged in again ! Be very careful so that no pin can break ! (If it does it's not the worst case, all chips are standard ones and you should get them for around a Dollar). These are PIN 9 of U 18 PIN 10 of U 6 PIN 3 of U 5 Be careful to choose the right PINs. Then put the chips back in the sockets, may be you have to cut the PINs a little bit so that they have no contact to other chips !!! Then connect PIN 3 of U 5 with PIN 15 of U 15 PIN 10 of U 6 with PIN 9 of U 15 PIN 9 of U 18 with PIN 7 of U 18 Now you're only have to plug in the RAMs (of course the new 4464 ones). Then put in power and monitor jack and switch on the computer. When the "READY"-prompt is shown the upgrade is completed - turn computer off, put it thogether ( keyboard and so on ) and run the self test - 48 K of memory are shown . If the self test is running or the charakters look strange, something with the multiplexers must be wrong - check if you have choosen the right pins. If the computer will not start up - turn off and check all connections. If have upgraded now two 600 XL this way and have had no errors (except one choosing the wrong PIN for the multiplexers - but this is causing no damage and now it runs very good ). I've only shown a very cheap way to upgrade a 600 XL - I'm not guilty if you will do anything wrong and so be careful !!! Matt