>That circuit will destroy the zener diode and/or the thyristor gate when
 >an event occurs and it will have 0.6V voltage drop through the transistor,
 >dissipating power. It is not self resetting (it could be with that parts
 >count). Just an opinion.
Is that due to the junction between the zener Anode and the gate of the
SCR? If so, just add a resistor there. No biggie. Everything else is
protected by resistors.

 > >
 > >-------+-----------C E----
 > > | B
 > > +---/\/\/\/---+
 > > | |
 > > --- ---
 > > /Z\ Vz = 5.x \ / SCR
 > > --- ---
 > > | /|
 > > | | |
 > > +-----------+ |
 > > | |
 > > / |
 > > \ |
 > > / |
 > > \ |
 > > / |
 > > | |
 > >-------+-------------+-----

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