digibloke wrote:Interesting. I've always been under the impression that LCD watches had pretty much instant shutdown once a battery stops supplying the required voltage (as opposed to LEDs which tend to get dimmer displays as the batteries run down). I guess it's feasible that a weak battery has caused my 8:17 after all (the oscilator circuit is fine so it wasn't a quartz failure).
It depends on where the "weak point" of the circuit is. If it's the oscillator that fails first with decreasing voltage, things can happen as described.
It's the same thing that happens to LED watches when they "freeze" and show a single bright digit: no oscillation = no multiplexing.
However, it's just an idea - I haven't ever observed this behaviour on any LCD watch (but on other circuits with LCD) - but I haven't seen any "burnt-in" LCD segments either.
More thoughts on this:
Some LCD watches (at least older ones) use a charge pump circuit to generate a higher voltage (~5V) for the LCD, also driven by the oscillator. So if the oscillator stops, then the charge pump also stops and there is no LCD voltage, thus no harm can happen.
If the watch in question has one 1.5V battery, then it's likely to have such a booster circuit. A 3V-driven watch usually doesn't need one as 3V is enough for the LCD.
Just for "fun" you could try to slowly reduce the supply voltage until the watch fails and see whether the display freezes or goes blank.
digibloke wrote:I least I can be pretty sure as to what time it was when the display developed its problem.
Like in Hiroshima when all clocks stopped at the impact time because the bomb's EMP magnetized the movements.