838-MX99 Replacement Keyboard (PRE-ORDER)

MX99 Keyboard - A Modern Mechanical Upgrade for the TI-99/4A!

THIS IS A PREORDER - PCBs, components, keycaps, etc. will not be ordered until after the pre-order closes. 

PREORDER will close on August 16, 2026.

Please read the entire description, it explains various options that can be selected at the bottom.

STLs for printing the brackets/adapters and MX99 keycap SVGs are located at the bottom in the Downloads Sections.

Please note that all MX-99 Keyboards even unassembled versions will include a 6U stabilizer bar since these are so hard to find.

The MX99 keyboard is designed to be used with standard MX keycaps for OEM profile.  If you are providing your own keycaps and choose a different profile the brackets will not be at the correct height.  The MX99 can also be used with original TI ALPS keyboard keycaps with the appropriate adapters (provided in the STL file download).

I do not have a Mitsumi keyboard, so I did not make a keycap adapter for the Mitsumi.  You may be able to use Troy's from his keyboard project, but it may need modified for height.

https://github.com/visrealm/keyboard4a99/tree/main/doc#bill-of-materials

The MX99 Keyboard is a complete, drop‑in mechanical replacement for the aging TI‑99/4A keyboard, engineered for reliability, modern usability, and long‑term serviceability. Built around 100% genuine MX mechanical switches, the MX99 delivers a crisp, precise typing experience while preserving full compatibility with the TI‑99/4A system.

This isn’t just a rebuild—it’s a thoughtful modernization of the original TI keyboard, adding features users have wanted for decades while maintaining the machine’s classic feel.

NOTE --- If choosing no options but the PCB, which is the default option, it will come assembled with all SMD circuitry and pre-programmed microcontroller with the latest firmware.  All purchased will come with a 6U stabilizer bar as these are hard as hell to find.

Key Features

100% MX Mechanical Switches

Every key uses industry‑standard MX switches for long life, smooth actuation, and easy replacement.

Choose between Cherry MX Blue, Cherry MX Black or Cherry MX Brown key switches.  See below for how each one differs.

⟵ NEW Destructive Backspace Key

A true destructive backspace—finally bringing the TI‑99/4A in line with modern editing behavior.

Integrated Backlighting System

Selectable OFF / LOW / MEDIUM / HIGH brightness levels. The keyboard remembers your last setting and powers up exactly where you left it.

Smart Microcontroller Integration

On‑board microcontroller handles:

• Alpha Lock logic

• Saving your Alpha-Lock state for next power up!  Just hold down the Alpha Lock key for 3 seconds in its current state to save for future power ups.  When the alpha-lock key begins flashing, the setting has been saved.

• Backlight control

• Destructive backspace behavior

• Future expandability for custom firmware features

Extra Power & Ground Contacts

Designed for stability and accessory support, including add‑on modules.

SMD Pads for TI‑99 USB Keys

Built‑in solder pads allow direct connection of TI‑99 USB Keys hardware—no adapters or rewiring required.

Power Requirements

The MX99 Keyboard requires a regulated 5V power source and must be tapped from the TI‑99/4A’s existing power supply. All logic and backlighting operate from this external 5V feed.

A Modern Keyboard for a Classic Machine

The MX99 Keyboard brings the TI‑99/4A into the modern era with mechanical precision, intelligent control, and quality‑of‑life improvements that make daily use smoother and more enjoyable. Whether you’re restoring a vintage system or building a fully modernized TI‑99 workstation, the MX99 is the keyboard the original machine always deserved.

I have made a video showing it in action on both the black and beige consoles.

 838-MX99 Keyboard for the TI-99/4A & 99/22

With the added 2 keys, the spacebar had to be reduced to a 6U.

Please note that with ABS plastic beige keycaps the LED even on the lowest settings will show almost like an x-ray effect on the top of the key.  This can be solved with some acrylic paint and a QTIP or small paint brush on the inside of the key.  Don't get any paint in the MX key switch mount.

There are options to be able to use original TI ALPS keyboard keycaps.  This will require adapters to be 3D Printed as well as extenders to be used with the special keys that will need to be purchased as an option.  The special keys include: 6U SPACEBAR, DESTRUCTIVE BACKSPACE, BACKLIGHT CONTROL keycaps.  If using the keyboard with ALPS keycaps, it is recommended to solder the switches and LEDs directly to the PCB.

Selectable options when purchasing:

Add Keycaps - this one is simple, you can either select no keycaps as you will provide them, Black Backlit Legend Keycaps (shine through legends), Black Laser Engraved or Beige Laser Engraved.  Both laser engraving are done on ABS keycaps.  The beige is very light and if using LEDs for backlighting they will shine through.  They will need to be painted inside with something like flat black acrylic paint to block the light completely. 

NOTE*** - Please be aware the beige offered is a very light beige and not as dark as the original TI Beige Keycap color. 

Add 3D Printed Brackets - If you don't want to print the 3D printed brackets and want me to do it.  There are 2 different options for the brackets if you want me to print them.  Standard MX style which will be used with MX keycaps or the ALPS bracket that can be used with TI ALPS keycaps from an original TI ALPS keyboard.  Are included in the linked zip file.

Add 3D printed ALPS Adapters - If you don't want to print these and you will be using original TI ALPS keycaps these will be needed.  Are included in the linked zip file

Light-blocker Paint - For the laser engraved ABS keycaps specifically the beige, since they are so light they do not block the LED light under the keycaps and it will shine through the entire key, not just the edges.  If you want me to paint it with light blocking acrylic paint then I will, but it's tedious.  I suggest 2 coats if so.  The paint will be on the inside of the key, mainly the top inside surface.

Add MX Key Switches - Allows you to choose if you want to purchase the MX key switches from me, there are options for different colors and based on the color chosen will change the sound and how they feel.  See the table above in the description to make your decision.

Hot-Swappable Option - This if chosen will make your keyboard into a hot-swapable keyboard.  The MX key switches and LEDs will not be soldered in.  This is not cheap to do, but if you like the easy of swapping key switches or LED colors then this is for you.

Standard Keys Backlight LED Color - This is simply explained, pick a color of the LEDs that I can provide if you want them.  This is for all the standard set of keys for a TI-99/4A, does not include to two newly added keys (Backlight Control and Destructive Backspace keys).

New Custom Keys Backlight LED Color - This is to pick the color for the Backlight Control and Destructive Backspace key LEDs.

Assembly Test - Assembly/Test if you want me to do the assembly for a hot-swappable keyboard or a non-hot-swappable keyboard.  Please note that even if you select for me not to provide assembly and testing, all SMD components will be assembled and the latest firmware loaded onto the microcontroller.

Add Keycap Puller - Add a 3D printed keycap puller for use with MX keycaps.

Add AVR USB Programmer - From time to time I will release new firmware to address any bugs to the code.  You can add the required USB Programmer to be able to update your MX99 keyboard.

Add Screw-In PCB Stabilizers - Add screw in stabilizers for use with the 6U spacebar.  If providing your own stabilizers ensure you purchase screw-in stabilizers, not the snap-in kind as those are designed for a keyboard plate and will not work on a PCB.

Add Special Keys - If you have chosen to provide your own keycaps or will be using the TI ALPS keycaps you will need the special keycaps.  These keycaps include a 6U SPACEBAR, DESTRUCTIVE BACKSPACE and BACKLIGHT CONTROL keycaps in beige or black.

• Model: MX99
• Brand: 838 Designs