In the end we also managed to get a nice TI-99/4 with internal speaker and volume control. In this photo a 32Kbyte memory expansion and an RS232 interface complete the set.
Here are the original manuals and the masks to use for playing or teaching.
A detail from the inside, the PCB with an operational amplifier, used to drive the internal speaker via the volume slider potentiometer, which is located on the bottom of the TI-99/4.
Compared to all the others, this version has a very important peculiarity to keep in mind: the power supply that provides the three voltages (+12vdc, +5vdc and -5vdc) is not located inside the computer but outside in a plastic box as shown in the photo.
It is important to note that the 4-pin connector has a different sized pin than the other 3 pins.
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