HP 30b Mode Settings

[robocop]

I had the same issues with my HP 30b and HP20b.
Looking for a solution I stepped into this site.
I solved the problem for now by applying a very fluid and fleeting contact cleaner/spray carefully (not to much) into the battery compartment while the buttoncells where in. Then I moved the cells a little bit with my fingers to rub away possible oxidations.
By the way this method helped also on my HP 35s with - in my case - the 0 button. Here I applied 2-3 times the cleaner directly on the 0 button on the key panel (in the space between). The area around I simply dried with a paper tissue.