TI-58C and TI-59

[Xorand]

So I found some specs for power supplies in the TI-58/59 series.

The battery voltage is (nominally) 3.6V. There is a voltage board that also creates -10V and -16V. I found where to measure those on the TI-58 and they were -6.5V and -12.5V, respectively.

I was using my variable DC power supply to provide the 3.6V input to the calculator, so I carefully ramped up to 3.9V input. Interestingly, the two voltages remained somewhat constant if not dropping just a little. Hmm.

For reference, I pulled apart a working TI-59 that I have in the current parts pile (missing a card reader) and performed the same testing on it with about the same results. However, the display on the TI-59 was fairly brighter than the TI-58.

The TI-58 is a very early model (date stamp 4677, which is around November of 1977 - they were introduced in May of 1977). Wonder if they were just using dimmer LEDs in earlier models. My good TI-59 has the brightest display of the bunch of calculators but is a 1982 build.