Re: 465B strange ripple


On Wed, Feb 24, 2021 at 9:55 AM Stephen <> wrote:

I forgot to mention that while in XY mode, I NEVER get a clean dot. It’s
always a very small line about 3 mm wide.
Wide or tall or both?
If the noise only manifests in one of X or Y in XY mode then you'll know
that it's sneaking into the respective part of the block diagram I
mentioned above. You can then go look for supplies that are unique to that
part of the block diagram, or generally go noise hunting there.
If you see the noise spoiling both X and Y, it has to be coming from the
vertical attenuators or preamps.

BTW: Do you know for sure that the outlet the scope is plugged into has a
good ground?
Well... none of my 9 other scopes do that. Although I may have noticed
that on my 466 as well...
I’ll have to recheck.
If you have a DMM that you trust with line voltages, you can measure your
outlet ground. Start my measuring the AC voltage from line to neutral. Then
measure the AC voltage from line and neutral to ground. Neutral to ground
should be as near zero volts as makes no difference. Once you've determined
where the neutral is, you can measure the resistance from ground to
neutral. I wouldn't necessarily recommend doing this with any $4 rinky-dink
DMM, but I know that e.g. my Fluke 87 is protected and will fail safely
even if I measure across the line in resistance mode :).

Alternatively you can throw the breaker and just measure the resistance
from ground to neutral - that should be safe.

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