I have built an Apple 1 replica which is based around a 6502 processor (R6502AP).
It functioning rather unstable (sometimes it works, sometimes it doesn't - it won't always boot properly) so I'm trying to figure out the cause.
When I look at the power line with my scope, I notice a huge voltage ripple starts right after the 6502 boots (when it's reset).
It varies from Vpp = 300 mV up to around 450 mV, so it's pretty significant.
The clock signal is a clean square wave at around 630 kHz (currently produced by an Arduino as I'm still waiting for a proper 1 MHz oscillator).
All the IC's have 100nF bypass caps close to them.
I'm pretty confident this ripple is causing the CPU to be this unstable. My question is two fold:
1) Is this ripple normal behavior? If anyone has built a 6502 computer, maybe you can tell me if this also occurs in your build.
2) If it's not normal, how can I counter it? I have tried adding electrolytic capacitors of varies values close to the CPU's power line, but it doesn't seem to help.
Update: maybe this helps - I remembered I had an Atari 2600 laying around which contains a 6507 CPU that comes from the same family as the 6502. The Atari 2600 also has ripple voltage on the CPU power line once it boots. It peaks at round Vpp = 300 mV.
So maybe it is normal?