I may be better off seeing if it's just measurement "sloppiness" that's giving me those readings.
Pertinent article:
PIN 7 on J119 is ground and a much shorter path than using the ground lead clipped to a heatsink. It's worth seeing if I can eliminate some of that noise with better measurement techniques rather than trying to fix something that may not be broken.
Thanks,
Barry - N4BUQ
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----- Original Message -----
From: "David davidwhess@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Sunday, April 3, 2016 2:48:40 PM
Subject: Re: [TekScopes] Re: 2465B U400 Availability?
When making low level measurements, do a sanity check by applying the
probe tip to the same location as the ground clip and then to a ground
near the measurement location. If the noise still shows up, then
either the ground clip is too long or common mode noise is traveling
between the DUT and oscilloscope via their power line ground
connections. Another thing to check is that probe, ground lead, and
test lead positioning does not affect the measurement.
On Sun, 3 Apr 2016 14:10:20 -0400 (EDT), you wrote:
...
Regarding ripple measurement: When measuring (using the 2445), I don't
exactly see what appears to be PS ripple, but lots of low-level noise (when
viewed with LINE triggering). I assume that's CPU and/or other digital
noise. It presents itself as a band of about 5mV. Is this normal? I have
a 10x probe inserted into J119 and the ground clip attached to one of the
heat-sink fins on one of the Uxxx modules. I'd think this "noise"
shouldn't be getting back into the rails but perhaps it's normal (or,
perhaps, something wrong with the way I'm measuring it)?
One of the rails (I don't remember exactly which one and will have to check
again to find that out) exhibited a small "double blip" that appeared to me
like it's coming from a typical unfiltered full-wave bridge but it was only
a few mV. Not sure if that's normal but I think it was within tolerance.
...
