Task: Upgrade an Atari 600XL to 64K of RAM
Needed: 64K RAM board from Lotharek, soldering iron, wire
Time: 1-2 hours
Many Atari 8-bit computer fans love the 600XL given its small footprint. It is perfect if you don’t have a lot of desk space. The 600XL is very similar to the 800XL with a few important exceptions. First, as mentioned, it is smaller. Second, it only has RF video out. Third, it only has 16K of RAM which means it won’t be able to run some of the 48K and 64K games and software which were popular on the 800 and 800XL. Fortunately, it is relatively easy to upgrade the 600XL to 64K of RAM. Below are instructions for installing the 64K upgrade from Lotharek.
This is a pretty easy mod which should take an hour or less if you have a workbench with everything set up and ready to go. It took me about two hours including settling on a plan of action, setting up my workspace with soldering iron, doing the mod, and cleaning up.
The first step is to purchase the upgrade. You can order it directly from Lotharek for about $20 plus shipping. This is the way to go if you are in Europe. Since I am in the U.S., I got mine from the Brewing Academy for $27 with some savings on shipping. The kit only includes the RAM board.
The second step is the preparation of your workspace. You will need a soldering iron to connect one wire along with screwdrivers, needle nose pliers, etc.
The third step is to open up the 600XL and remove the top RF shield. Mine had a combination of screws and nuts which needed to be removed. There are also some tabs which need to be straightened. I always find these a pain to get off. I discarded my RF shields. Once the top shield is off you can then remove the two screws holding the motherboard to the case and remove the motherboard. These are also a little tricky to remove given the SIO and joystick ports.
The third step is to remove the two RAM chips and the Sally 6502 processor chip (see image below for locations). Note that we will not need the RAM chips further. You can hang onto them for other projects. We will need the CPU so keep it in a safe place. The good news is that most 600XLs seems to be socketed so these are easy to remove with some gentle lifting. I use a small flat tool to wedge them up from each side.
The fourth step is to seat the 64K board from Lotharek in the CPU socket. The Atari symbol goes tot he right toward the joystick ports.
The fifth step to solder a wire from the CI connection on the 64K RAM board (upper left above EXT) to the 16 pin on the MMU (see below). The MMU is the chip just below the beige plastic cartridge shield. Find the 16 pin by counting counter-clockwise from the bottom left of the MMU. I needed to take the cartridge shield off to have enough room to solder. I put a bead of solder on the exposed flat pin of the MMU and then heated that to attach the wire. Be sure to bend the wire so it doesn’t create pressure. My first attempt popped off. Note that soldering directly to the pin of a chip is a bit of a shortcut and not generally recommended. It is usually better follow the trace on the circuit board and find a via where you can solder the wire. More likely to stay put as well!
The sixth step is to seat the 6502 CPU to the 64K RAM board. This is a little tricky since all the pins have to line up exactly. I was able to get this in by getting one row part way in and then gently putting pressure on the remaining pins until they went in.
The seventh step is to reassemble the 600XL and test the RAM! A quick way to see if everything is working is to boot into the self test and run the RAM test. Note that the self test will only test up to 48K of RAM. This will be your first indication everything is working. I also use a Supersalt cartridge to test all 64K. Those results passed.
This is a pretty easy mod and recommended if you want to use a 600XL as your primary computer. I would like to do a UAV mod next since the 600XL only has RF video out. This will require a new monitor port and a case modification to make the RF hole bigger.