Remove the cover from the computer by releasing the six screws on the bottom
of the unit.
Lift the top case slightly and press it back to reveal the two ribbon cables for the keyboard and LED assembly.
Press each of these connectors back to slide them off. Once the cables are
disconnected, you can remove the top case completely.
Once the top case is removed, you must remove SIX screws to free the main PCB from the bottom case. Three of these screws are in the front, three in the back.
Once the main PCB is free, lift it, along with the RF shield out of the case by tilting the front of the PCB upwards.
The bottom half of the case has two parts that will require re-assembly later.
Most 1200XL cases have rivets holding the two halves of the RF shield together. To remove these place the PCB/RF shield assembly on a table and press down on the top of each rivet with the handle of a small screwdriver.
Once you have popped out all the rivets the top shield should lift off without any resistance.
With the top half off, lift the PCB out of the bottom half and set the RF shield
1200XL PCB LAYOUT
Now that you have the main PCB out, you will need to remove the old parts from the board.
Locate the OS ROMs in the photo to the right. Remove these from their sockets.
Look carefully at the sockets that were holding the 1200XL OS ROM set.
On most 1200XLs, there are 24-pin sockets installed. You will need to desolder these sockets and replace them with the 28-pin sockets that were included in your kit. If your 1200XL already has 28-pin sockets installed, just skip the next paragraph.
After carefully replacing the sockets, put the old OS ROMs back into the sockets and test the computer. Note that with 28-pin sockets installed, you have to insert the 24-pin OS ROMs in the right-side of the socket, with two rows of pins showing to the left side of each chip.
If the computer works normally then the sockets are installed correctly. If you have any problems check your work and do not proceed to the next step until the unit is working again.
Once the 1200XL is working and the new sockets are installed, remove the OS ROMs and MMU. The MMU should already be socketed.
Place these chips in the anti-static container your upgrade was shipped in, if you ever want to restore your 1200XL to its factory configuration, you will need these parts.Step #7
Look for W7-W13 just to the right of the cartridge port.
Desolder and remove W7, W8 and W9. Take the jumpers you removed and install them in positions W11, W12 and W13.
Turn the PCB over and using a small length of wire, connect the top pad from the W6 location, the jumper you just removed, to pin 23 of the CPU.
With the PCB turned over, the CPU pad layout has pin 21 at the top-left. Count
two pins over to find pin 23, as shown in the photograph.
Take the resistor included in your kit and solder one end to pin 20 of PIA. Solder the other end to pin 11 of PIA. Do this on the bottom of the PCB.
With the PCB turned over, PIA is located directly below the CPU, as shown in the photograph.
You can place a short piece of tape under the resistor to prevent any shorts, or place heat-shrink tubing over the resistor to insulate it.
Take another length of wire and connect one end to pin 11 of PIA, where you just connected the resistor, and the other end to pin 18 of the MMU socket.
A wire set for three solder connections is included with your kit.
This harness has four wires, one red, one white and two black. The two black wires for are the same signal, so cut off one of the black wires close to the harness connector, it does not matter which one.
Locate the GTIA IC on your 1200XL main board using the diagram above.
Connect the white wire to GITA pin 33.
Connect the black wire to GTIA pin 30.
Locate the 74x138 IC on your 1200XL main board using the diagram above.
Connect the red wire to 74x138 pin 14.
Take the new MMU provided in your kit and place it in the socket that held the old MMU.
Take the BASIC EPROM provided and place it in the TOP OS-ROM socket, just below the cartridge port. This chip will appear to be missing one pin. This is normal.
Remove the MyIDE upgrade module from its package and insert the board into the LOWER OS ROM socket.
The photo on the right shows the correct orientation of the OS board in the Atari. Do not insert the board backwards or it will be damaged. Damaged boards will not be replaced.
DO NOT APPLY EXCESSIVE FORCE INSERTING THE BOARD.
If you encounter too much resistance inserting the board into the socket, check the alignment of the pins in the socket and make sure it is correct.
Press straight down on portion of the board over the OS ROM socket to insert it. Do not insert the board at an angle or one side at the time, as this will bend or break the gold pins.
Once the board is inserted, look underneath it to verify all the gold pins are in the socket. If any are hanging over the edges then remove the board and re-insert into the socket correctly.
Now that the module is installed, you must plug in the wire harness to the correct location on the MyIDE PCB.
Please see the orientation diagram above before plugging in the wire harness.
You must plug the wire harness into the multi-pin header on the PCB that is facing the rear of the 1200XL. Align the harness as shown in the orientation diagram above with the RED wire closets to the '*' printed on the PCB near the header.
Attach the power and monitor connections to the Atari and turn it on.
The system should start normally, and you should reach BASIC, Self-Test or MyIDE boot screen. ("Waiting for IDE")
If the system does not function normally, check all connections.
Reassemble system and re-test. On some models you may have to omit the RF shield or cut a hole in it.
Thanks to Larry White for use of his 1200XL installation photos.