Help needed reviving a 30b

[mfleming]

Sadly, I think you now have a doorstop with buttons. I'd have to search for the post, but I do recall a warning that the calculator CPU will be damaged by a 5V applied signal, or a voltage on any pin that is more than about half a volt above the positive supply.

A number of programming schematics show a series resistor on the program lines so that a current flowing through the resistor will create a voltage drop to a safe level at the chip end. That arrangement is recommended if you power the calculator from internal batteries, so you won't run afoul of the second condition above when using 3.3V logic signals in combination with low batteries. Somewhere I downloaded such a diagram from a post on this site.

Sorry to be the bearer of bad news