Found the problem. The negative probe clip had a small piece of film preventing good ground connection.
Now I would like to get some mini-grabber or small alligator clips that would mate with this connector that is captive on the differential probe. Looked through the Pomona catalog without success.

Now I would like to get some mini-grabber or small alligator clips that would mate with this connector that is captive on the differential probe. Looked through the Pomona catalog without success.

> The negative probe clip had a small piece of film preventing good ground connection.
Ah, new stuff. Even probe clips need "break-in" ;') Glad to read that's it, rather than my guess.
Ah, new stuff. Even probe clips need "break-in" ;') Glad to read that's it, rather than my guess.
A very good reference on scope probes and probing techniques: http://eelabs.faculty.unlv.edu//docs/guides/ABC_of_Probes.pdf
Excellent advice on grounding starting on page 36.
Safety issues starting on page 44.
Speaking of safety concerns, I once say a guy using a Tek 475 dual channel 100Mhz scope which was expensive in those days, accidently drag a dangling probe ground lead across a 100kW power supply 300v rail. Needless to say, the scope was absolutely destroyed. Lucky he didn't get hurt.
Excellent advice on grounding starting on page 36.
Safety issues starting on page 44.
Speaking of safety concerns, I once say a guy using a Tek 475 dual channel 100Mhz scope which was expensive in those days, accidently drag a dangling probe ground lead across a 100kW power supply 300v rail. Needless to say, the scope was absolutely destroyed. Lucky he didn't get hurt.