Yes, see if you have a pulse on pin 15 now. If so, then it was bad IC or socket connection, etc. Don't worry how noisy a signal is. I have a 200Mhz scope and very surprised how much noise is present on signal paths. TTL is just transition logic so the window is around 1V to 4V and noise outside of that doesn't seem to matter. That's just my observation. So now you get just one beep at power on? You might want to connect your keyboard, do a reset to get one beep, type some random keys and press return to see if you get a beep for syntax error. That would be a major step forward. It is very likely you have multiple problems.