Getting Color Output out of a TI-99/4A #VintageComputing

Hans Hübner found a vintage TI-99A machine cheaply on sale on an auction site and bought it. To get color output from the computer, an adapter circuit called TMS-RGB designed by Nicholas Piegdon was procured.

The TMS-RGB is a generic RGB converter for systems using the TMS9929A chip, i.e. the TI-99/4A, some MSX systems and the ColecoVision. It is a tightly packed PCB with surface mounted components meant to be soldered onto the solder side of the PCB of the machine to be converted.

The TMS-RGB converts the YPrPb signal to RGB + Sync, but it does not change the overall timing. This means that one either needs a monitor that can deal with TV format RGB signals (i.e. one that has a RGB SCART Input or a CBM 1084), or an upscaler that converts the signal to match the expectations of a more modern computer monitor. I bought a cheap GBS-8200 upscaler board which produces a VGA output and it worked fine.

In fact, the picture quality that I get with this on my TFT monitor is just awesome. The pixels are crisp and the is no blur, jail bars or ghosting. I can recommend the TMS-RGB board to anyone who wants to equip their TMS9929A based hardware with a better video output. The overall cost for the PCB’s, components and the upscaler board was around 70 Euros.

See the details in the post here.

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