[sdiy] How much is too much?

[mark verbos]

On a power supply for digital electronics, how much ripple is too much? 
When do the parts just freak out? I have an RSF SD140 drum machine that 
doesn't work and I have no schematics. I have just checked the 5 volt 
line and there is a little ripple on it. Would that make the thing not 
power up? I'll just go ahead and change the caps on it, but I'm curious 
anyway.

Mark