This great forum has inspired me to try to repair my 34c, which I have had since new around 1981. So far, thanks to all the helpful posts, I have managed to rebuild the battery, open the case, and repair the lost digit in the display. However, I have made no progress dealing with Pr Error every time it is turned on, and STO ENTER returns Error 9. Clearing Error 9 returns 0.0000. It seems to have no memory at all - I cannot program or use storage registers (the stack does work). This is a solderless unit, and I have double checked chip positions and locations (I'm sure I am the only one to have opened this one). I have twice cleaned all the flex PCB connections. One other oddity - I cannot enter decimal point from the keyboard, although I can enter Pi. It does display decimal points correctly resulting from division of integers.
Thanks to all who have shared their knowledge,
David Derrer