HP-48SX (attempted) repair by Ben Heck

[ijabbott]

(09-25-2021 04:07 AM)GreyUser Wrote:  Oh, one last thing. Anytime you have an S/SX or early G series machine opened, be sure to remove the zener diode between the lcd boost mosfet and the boost inductor (the round blue blob). The original purpose was for reverse polarity protection but they don’t work because they will fail shorted when batteries are installed backwards and when it has failed, it will just drain your batteries in a couple days or less. Just cut the single bottom pin with a knife or small cutters and hinge up repeatedly until the other two leads fracture and it falls off.

Whilst you have the case open, I wonder how easy it would be to fit a Schottky diode in series with the battery to provide some proper reverse polarity protection?