[wwest]

So, question, if the 82 volt zener were open, not limiting the voltage across the "flyback" transformer primary to ~70 volts, what would be the final charge voltage for "the" capacitor..??

What might be the "target" design parameters, given a good, even excellent, design engineer, for the power handling parameters of that 10 watt 82 volt zener..?

Just what design engineer would have the expectation of the design having to operate and survive continuous operation with the battery supply voltage well above design expectations..22 volts such as you state ?

So, isn't it likely that the zener diode is operating very near it's upper power disapation limit with the battery supply voltage on the "normal" high side, <15 volts..??