HP-48SX (attempted) repair by Ben Heck

[GreyUser]

A zener isn’t desired or needed. It was so problematic and a cause of warranty claims that HP simply eliminated it on all later model G/G+/GX models.

I suppose you could install a series Schottky diode for true reverse polarity protection and live with 0.3 volt drop. But, it’s not necessary as the power supply and processor survive reverse polarity of alkaline AAA cells.