838-MX99 Replacement Keyboard
MX99 Keyboard - A Modern Mechanical Upgrade for the TI-99/4A!
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 the SMD circuitry.
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.
| Switch Type | Feel | Actuation Force | Sound Level | Behavior | Best For |
| MX Black | Linear (no bump) | ~60 g | Quiet | Smooth, consistent travel with no tactile feedback | Gaming, stabilizer-heavy keys, users who prefer firm keypresses |
| MX Brown | Tactile (light bump) | ~55 g | Quiet-Medium | Noticeable bump at actuation without a click | General typing, mixed use, users who want feedback without noise |
| MX Blue | Clicky + Tactile | ~60 g | Loud like vintage keyboards. | Strong tactile bump with an audible click mechanism | Typing, retro feel, users who want maximum feedback |
⟵ 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.
- Availability: Pre-Order
- Model: MX99
- Brand: 838 Designs