TOS 1.04 Upgrade 2 chips set version
Before purchasing this 2 chips kit, make sure your motherboard is compatible for such set.
Some versions of motherboards only have 6 support fitted for this 6 chips set version. Other motherboard will have the ROM chips directly soldered to it. No supports.
Open your Atari and check your motherboard before purchasing any TOS ROM set.
Although the fitting of these is a simple task, please be sure that you know what you're doing before fitting.
Some motherboards indicate which Rom is which (Hi-0, Hi-1, etc…), if your board does not have this information, but only Uxx, Uxx… then look for the information online. A search for pictures will show you the correct placement.
Some motherboards are designed to accept 2 chips and 6 chips sets. On these boards, 3 solder pads are present to configure the board to use 2 chips (1M) or 6 chips (256K). You must make sure you configure the board to 2 chips (1M). This may require soldering.
in orange, make sure the 1M solder pad are set.
6 IC supports for 6 chips set
Be extra careful when removing your ROM chips. Take your time not to bend any pins.
You can also place a sticker on them to mark which one is which. It will be helpful for future use.
Be also super careful when you insert the new ROM chips. Take your time and make sure no pins are bents.
See the diagram below for the orientation. Pin one is on the same side as the semi circle marking of the DIP support.
The 2 ROMs have labels under them L and H. L for Low ROM and H for High ROM. You should use them to place them on Lo-0 and Hi-0 supports.
Here is an example of 2 ROM chips fitted on an Atari STF motherboard:
Tri TOS 1.02, 1.04, EmuTOS
If you buy the ROMs from this shop already programmed with TOS 1.04, two other banks inside the OneROM will be loaded with other version of TOS.
The default bank 0 is TOS 1.04
Bank 1 is TOS 1.02 in case you wish to go back to the original TOS
Bank 2 is EmuTOS. It will be the latest EmuTOS version available at the time.
You could solder some headers and use jumpers to select the banks. If you do so, you may have to cut the header solders under the PCB with a fine cutter as shown on the pictures.
Proceed only if you are comfortable with soldering. This part is optional. The OneROM will provide TOS 1.04 out of the box.
You can use jumpers to select your bank or a switch.
Use a 3 positions switch to select any of the 3 banks.
You could use a very small slider switch and hide it somewhere like in the example below: A small 2 positions slider switch hidden under the cart port to select between TOS 1.04 and EmuTOS.
More about OneROM
OneROM is an open source project. The aim of the project is to offer a flexible replacement to old ROMs for our retro systems
The OneROM project is available here: https://onerom.org/
The OneROM used for the Atari TOS 1.04 kit sold on this website are 28 pins "Fire 28A". You can reprogram them using the OneROM studio available on https://onerom.org/
The only difference with other OneROM you may find elsewhere are the pins. The pins used here allow a much lower fitting on the Atari motherboards. This setup will allow you to fit back the metal shield.