On Fri, Jun 7, 2019 at 4:44 AM Curious Marc <curiousma...@gmail.com> wrote: > > Thanks, I’ll see if I can find replacements. You can easily see how they get > zapped: they are 2.5V chips, the NiCd battery *is* the voltage regulator. > Charging circuit is a simple diode connected to 5V via a resistor. Battery > dies, goes high impedance, somebody plugs it in to try it out and poof! Clock > chip gets zapped by 5V.
HP were fond of using NiCds as shunt regulators at that time. The did it in many of their handheld calculators (HP20 series 'Woodstock', HP30 series 'Spice', etc). In those it wasn't normally a problem (the calculator electronics drew enough current to pull the voltage down) except in machines with 'continuous memory' (battery backed RAM). There, if the machine it turned _off_ the RAM is the only thing drawing current and it doesn't draw enough to pull the voltage down below the zapping level. -tony
