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