TI-99/4A PSU Modern Black US

High-quality Texas Instruments TI-99/4A replacement power supply unit (PSU). Designed specifically for TI-99/4A systems to preserve them in a pristine condition for years to come. Stabilized +5V/4.0A, +12V/2.0A, and -5V/0.5A DC ensure continued error-free operation of your TI-99/4A. Robust and sturdy chassis with LED-illumination and different styles and colors to chose from. Fully fused and electrically protected, with specialized 4-pin plug matching the original TI-99/4A PSU pinout. Requires a minor modification consisting of disconnecting the built-in TI-99/4A power supply board.

TI-99/4A PSU Modern Black US
  • Replacement power supply for Texas Instruments TI-99/4A

  • Stabilized +5V/4.0A, +12V/2.0A, -5V/0.5A DC output (requires disconnecting the built-in PSU board)

  • Over-voltage and over-current protection

  • Fused on AC and DC side and fully isolated

  • On/off AC switch on rear side

  • LED-illuminated high quality chassis

  • Potentiometer for adjusting LED brightness

  • Durable and thick cables on both sides

  • Runs cold

  • Weight only 0.6 kg (1.3 lb)

  • Compact enclosure with modern shape 125 mm x 59 mm x 42 mm (5.0" x 2.3" x 1.6")

  • Specialized 4-pin plug with +5V/+12V/-5V DC

  • US-standard 120V AC power plug (U.S., Canada, Mexico, Japan, and others)

A fresh start

TI-99/4A systems have sold in over 3 million units worldwide, an impressive number even by today's standards. However, unlike modern computers, tablets, and smartphones, a considerable number of TI-99/4A systems are still operational over 30 years after being introduced to the public. In proper hands they have a chance of surviving another 30 years. Yet a common failure among TI-99/4A systems is the power supply. This is specifically why we have designed a replacement TI-99/4A PSU. This series of power supplies gives your system a fresh start, minimizing the risk of damage due to an ageing factory power supply.

TI-99/4A PSU Modern Black US

Robust and reliable design

The TI-99/4A PSU was designed from scratch as a high-quality replacement for the original TI-99/4A power supply. It contains internal +5V/4.0A, +12V/2.0A, and -5V/0.5A DC switching power modules. The PSU is intended to replace the original built-in power supply board, thus a minor cabling rework is necessary (described below). The power supply has a sturdy custom-made chassis with an elegant LED-illuminated logo.

TI-99/4A PSU Modern Black US

Modern style chassis

The TI-99/4A power supply has a chassis design called Modern (as opposed to our C64 Classic series), and resembles a modern power supply with a slick shape of 125 mm x 59 mm x 42 mm (5.0" x 2.3" x 1.6"). It's a lot lighter and more compact than the original TI-99/4A power supplies. The TI-99/4A PSU chassis are available in colors black and gray.

Black vs. Gray chassis

All our power supplies are available in black and light gray. The performance between both types doesn't differ, it's a matter of taste. The LED and OLED displays (depending on the version) are generally black with white illumination, being more pronounced on the gray edition and giving an interesting color combination. On the other hand the LED/OLED display blends in the black version better, being barely visible when not powered. If at the point of purchase you are uncertain about the item version in the cart, please drop us a message with the desired chassis style, color, plug type and voltage (US/EU/UK/AU).

TI-99/4A PSU Modern Black US

Precision and dedication

The development of our series of Commodore, Amiga, Sinclair, Atari, Coleco, and TI power supplies has been driven by a sense of sentiment for retro-computing, combined with accuracy and dedication in creating electrical equipment to be proud of. It goes without saying, that the electronics has been designed by skilled professionals, thoroughly tested, and improved based on years of feedback from thousands of users. However, we have also put a lot of effort into the visual appearance of our power supplies. We design and manufacture our own enclosures with CNC and injection molding technologies. The LED and OLED panels are carved from PMMA to give a modern appearance to the power supplies. Hundreds of hours of designing and perfecting have been put into these devices, to create not only a safe and robust power supply, but also a satisfying visual improvement to your system.

TI-99/4A PSU Modern Black US

What else is out there?

The original TI-99/4A power supplies are very hard to get by these days, and often pose a reliability or even safety threat. As for other replacement power supplies, a handful of solutions exist on the market. Yet most of them are DIY-grade, lacking basic quality, electric engineering expertise, and safety features. The vast majority of these power supplies is recognizable by general-purpose plastic enclosures and internal components wired up in a true DIY style. Opening up a few of those power supplies was big motivation for us to design our Commodore C64, C128, Amiga, Atari, ZX Spectrum, Sinclair QL, TI-99/4A, and ColecoVision power supply series.

TI-99/4A PSU Modern Black US
TI-99/4A PSU Modern Black US

Safety first

Our TI-99/4A PSU is designed to be safe for the user, and safe for the computer. It's protected from over-current and over-voltage, and fused on both the AC and DC sides. Nevertheless, it's mandatory to say that this is a 120/230V AC power device, which should not be opened, tampered with, or used for anything else than powering an unmodified TI-99/4A computer. It's intended for indoor usage only, the maximum rated current should not be exceeded, and proper ventilation should be ensured. For reference, a picture of the opened power supply is shown below.


Do not connect this power supply to your TI-99/4A without doing the modification described below! This modification should be done by a skilled technician only. The original TI-99/4A expects 8V AC and 16V AC supply voltage, and the internal power supply board converts it to +12V DC, +5V DC, and -5V DC. The original setup is shown on the scheme below.

TI-99/4A PSU Modern Black US

Nowadays it seems unreasonable to build an external AC power supply and use the built-in converter board, which is usually 40+ years old. Therefore, our power supply generates +12V/+5V/-5V DC directly, meaning that disconnecting and bypassing the built-in PSU board is necessary. To do this modification, open the TI-99/4A, locate the cables to and from the built-in PSU board, and disconnect them.

TI-99/4A PSU Modern Black US

Finally, solder the four wires from motherboard directly to the input power socket, bypassing the built-in power supply board. Use a voltmeter to determine the voltages on the cables. The new PSU pinout is shown for reference.

TI-99/4A PSU Modern Black US

Double check the voltages before applying power to the motherboard. Incorrect voltages will definitely lead to irreversible damage to the motherboard and peripherals!