More Apple II fun - 4116s...

Well, I did more experimentation with the Apple IIs. I decided that, having one machine that worked fine, I could use it to test the RAM from the other two. I was surprised to find that of the 48 4116s I tested, nine were faulty enough that the machine wouldn't boot. My testing wasn't very thorough, so some may still be bad; on populating the original Apple II with RAM that seemed OK, it started up OK, but still behaves a bit randomly (hitting Enter makes random characters appear on the screen, it tends to suddenly change video modes, and drop into the monitor at times as well). My real question is - 9 faulty out of 48, spread across both machines, seems very high. Are 4116s that unreliable? Or perhaps they're quite sensitive to power supply problems? Mike.