HOW TO UPGRADE YOUR ATARI 600XL TO 64K RAM
THIS MOD IS COPYRIGHTED BY KEN SUMRALL. HOWEVER, YOU MAY FREELY
DISTRIBUTE IT, AND MODIFY IT, AS LONG AS THIS NOTICE IS INCLUDED
IN ITS ENTIRERTY. THE AUTHOR MAY BE REACHED AT THE FOLLOWING
You will need the follow parts to perform this mod:
(2) 4464 RAM chip, 64Kx4, 150ns or faster.
Additionally, you will need chip pullers, a soldering iron, and 3 small
pieces of wire. I used wire wrap wire when I did this mod.
If the chips on your 600XL are socketed, you're in luck, otherwise, you need to
first unsolder the following chips:
(1) 74S32 location U18
(2) 74LS158 locations U5 and U6
(2) 4416 locations U11 and U12
and put sockets on the mother board in their place to make the job easier.
Now bend up pin 9 on the 74S32, and put it back in its socket on
the mother board. Bend up pin 3 on the 74LS158 in location U5, and put it
back in its socket. Also, bend up pin 10 on the 74LS158 in location U6,
and put that chip back into its socket. The last two chips you need to
change are the two RAM chips. Put the 4464 chips into the sockets at
locations U11 and U12 on the motherboard.
Now you need to install 3 wires to complete the mod. The first wire should
be connected between pin 3 of the 74LS158 at location U5, and pin 20
of the parallel bus on the 600XL. The second wire should be connected between
pin 10 of the 74LS158 at location U6, and pin 18 of the parallel bus.
The third wire connects between pin 9 of the 74S32 at location U18, and
pin 45 on the parallel bus. That's all there is to it.