I hope you have a scanner or photocopier, there's a few things you may wish to copy that i'll bring with me. The spikes are absolutely no surprise, considering the mishmash of unbalanced gates with no consideration of propagation delays whatsoever. U28 pin 6.. hmm I couldn't say exactly what it is, there are 12mhz and 3mhz signals going through U76 (a pair of flip flops) which goes to U28 pin 5. The BUSAK signal will be at the vertical frequency (48.8hz) and will only be present when the screen is ON, at U28pin4. U28pin6 will be these two signals NANDed - whatever that results in. Perhaps bursts of 3mhz at 48hz. Whatever, it is the signal that allows the video circuitry to read the RAM during screen refresh times. Btw, this exact part of the system is what needs a mod I will bring to you. Once things are running, you MUST add this mod.