HP21 uses same RAM chip as HP25?

[calc-calcs]

Hi Jose,

The RAM chip was soldered onto the board, after removing it I put in a socket. None of the chips on the board of this calculator are on sockets, so corrosion as you describe it is not an issue. But I agree that it certainly happens on older test equipment, specially the ones using regular (non-machined) pin sockets, and simply reseating ICs often solves problems.

Update: Calculator is still fully working.

Alex