The Coleco Adam originally shipped with a printer that contained the entire PSU for the device. It generated 12V, 5V, & -5V DC voltages for the system to run on. Now it is increasingly difficult to find the printer to go along with the system. This renders them unusable.

This project is an internal PSU that can be mounted inside the standalone Coleco Adam. If you have an Expansion Module #3 version of the Adam, it can be used outside of the system as well.

This part was designed specifically to be non-destructive and once you have an assembled part, does not require any soldering. The DB9 connector on the standalone Adam is on a small cabled PCB. This board mounts in place of that and you internally connect that cable to the new PSU. Optionally, you could cut or desolder the DB9 connector and directly bridge across to the available pads.

For use with the Expansion Module #3 version of the Adam, the board can be externally plugged into the system. Based on feedback, this is assumed to be a much less common model and the design hasn't been optimized for this use. You may need to extend the DB9 connection to have enough clearance. A solid DB9 male to female adapter is encouraged over a cable for its better current capacity. If you do opt to use a DB9 extension cable make sure it is not a null modem cable!. Pins 3 & 3 on a null modem cable are swapped which will swap 12V and 5V going to your system which will severely damage crucial components.

This power supply is fundamentally a multi voltage DC-DC regulator. It takes in a 12V 3A power source and while passing through the 12V also generates 5V and -5V. The system itself has the following maximum power ratings:

• 5V - 2.75A
• -5V - 0.2A
• 12VI - 0.6A
• 12VL - 0.3A

(Taken from page 49 of the Adam Technical reference manual)

The 12V rail is split between inductive and logic loads on the system side. D1 allows for potentially high voltages to be recirculated but due to the shared ground at this time I'm not sure how useful this really is.

This power supply is capable of supplying the following with the DC-DC regulators:

• 5V - 5A
• -5V - 1A

These higher output capabilities combined with the ability to change the 12V external power source should allow all potential accessories to have sufficient power. The original maximum power rating is in total ~25.2W, using a 3A 12V AC-DC converter provides ample headroom for DC regulations losses.

This regulator is made using SMPS Buck regulators to reduce the 12V input to 5V and -5V. The -5V source is a standard buck regulators being used in a negative configuration. Care has been taken in the design and parts selection to maintain as much efficiency as possible. Despite this there will be power dissipation still and the board layout has taken this into consideration providing large copper pours where possible. Heat sinking should not be necessary as the parts should be, on average, drawing less than half of their maximum current in addition to the PCB cooling.

The physical parts selection for this as well as the layout design has kept in mind the ability to hand solder the parts. However, outside of the I/O, all parts are SMD and go down to 0603 sized passives. It is recommend that you have a solid background in soldering, but this is not an especially difficult SMD board to assemble. U2, is an SOIC-8 with a thermal pad which will likely be the part that will give beginners the most difficulty. Recommended steps are:

• Lightly tin the thermal pad
• Apply flux
• Place the part down, checking orientation
• Solder opposing corner pins
• Apply heat to the underside of the board while also applying pressure to the part
• Finish soldering remaining pins

I will be producing these indefinitely and making them available for purchase. They will be available on my website once I have assembled and validated the design.

The BOM is stored as extra fields in the KiCad schematic and can be exported from there. It is also included as a CSV file with the non-orderable parts removed.

I have also created BOMs on Digi-Key and Mouser as shared carts that you can order directly:

Digi-Key: https://www.digikey.com/short/p0tbzh Mouser: https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=6486fe3deb

BOM Errata: For v0.1 boards R4 needs to be changed to 1k instead of `0k. The BOM carts have not been updated to reflect this yet.

The parts selection vary slightly between vendors. Equivalent performance low cost parts were selected in each case.