Crazy 60Hz noise

A project log for One-instruction TTL Computer

A breadboard-able computer which uses only a single instruction - MOVE

justin-davisJustin Davis 11/29/2017 at 14:560 Comments

After getting my control shift register working, I noticed it's very glitchy and would race whenever the clock was low.  After some investigation, I found this on my board.

Not just a little 60Hz noise, but almost 150V of it.  I traced it back to my 5V wall-wart.  This picture is the ground on the wall-wart when it's disconnected from my circuit.  I have about 300uF of bypass on my board, but it can't mitigate this.  I have to imagine this is a bad wall-wart.  It's a Volgen model from Kaga Electronics made in China, but I bought it from Digikey, so I figure it's not counterfeit.  It's possible I fried it at some point, but I haven't noticed any events.  And it still measures 5V on a Fluke meter.

I connected my board up to a good adjustable lab supply and the problems stopped.  I measured it the same way with the same scope to make sure it wasn't a scope problem (but the glitchy behavior indicates it is not).  I would still like to have a dedicated supply, so I may order another brand from Digikey.  Has anyone else had similar problems with wall-warts?