🇺🇸 Texas Instruments TI 99/4A: Part 1 (First Look & Power Supply) [TCE #0533]
29I've had these machines for a while. They were never really a thing here in Australia, but they seem to be quite readily available and cheap in the US (if you ignore shipping). Let's start by looking at the power supply situation as it's a little different.
Part 2:
   • 🇺🇸  Texas Instruments TI 99/4A: Part 2... Â
The original 99/4 came out in 1979, with the original black & silver 99/4A coming out in 1981 and then QI "quality improved" version in 1983.
00:00 ... Start
04:00 ... Close look at key switch (stackpole type)
05:09 ... Comparing with QI beige model
06:50 ... Quick look at peripherals
08:23 ... Quick look at interfaces
10:05 ... Various power supplies
14:00 ... Quick comparison of four-pin & two-pin power
15:00 ... Power supply schematics
18:00 ... Checking the two-pin power supply board
20:24 ... Oh, different type of key switches & key cap text
23:30 ... Checking the four-pin power supply board
26:06 ... Close up of board types of power supply board
29:15 ... Channel outro/thanks
I love their keyboards, hence my slight obsession with them.
They're a little bit difficult to power as they use an odd four-pin connector that maybe died out in the 1970s (certainly not available in 2024). The original 99/4A power supply expects 16-18VAC and 7.5-8VAC input to internally generate +12VDC and ±5VDC. Later versions only require the 16-18VAC input.
But there are alternatives if you can't source an original US or Aussie power supply, or even if you do but want something modern:
[1] A replacement power supply that generates the DC voltages directly and has the correct plug. You will need to modify the internal power board to bypass itself totally:
hhttps://www.keelog.com/power-supply/#ti99
[2] Replace the internal power board with something like this that only requires a regulated 12VDC power supply. You can either replace the power socket with a 2.1mm socket or cannibalise the original plug:
hhttps://github.com/dabonetn/ti99psu-replacement
[3] Use a Mean Well GP25A13A-R1B as the power supply and remove the internal PSU board, wiring a 5-pin DIN socket to the internal cabling.
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