Diagnosing an Atari Lynx low battery circuit #VintageComputing #ReverseEngineering
Evan’s Techie Blog looked to diagnose issues with the low battery circuit on an Atari Lynx:
This voltage detect IC seems important to be always powered, and with the soft-power circuit of the lynx and the strange low side buck converter topology I have some question as to what it’s doing. Maybe it has something to do with the feedback circuit on the switching converter?
Oh. If I turn the voltage down below about 5v (when the switching regulator stops switching) the LED starts blinking. It was a low battery indicator this whole time. But that is a CMOS chip holding its output transistor on the entire time there are batteries in this thing. That has to have some power consumption impact. All to have a precise voltage detect IC for a low battery oscillator.
And the main power supply still uses just a zener diode to set the output voltage. I don’t think I will ever understand atari, they built this thing out of literal 2n3904 and 2n3906 parts like you would get at radio shack, then they overengineered the low battery blink and under-engineered the power supply regulation.
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