EEVblog #987 - Keysight U1272A Multimeter EMC Followup

Checking out the fix for the Keysight U1272A Multimeter EMC/RFI problem.
What did they change and why?

Grounding in mixed signal systems:

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[Audio_Simon]

I do most of my electonics on audio equipment and I've yet to find a case where coupling grounds via any kind of resistance or filtering helps. You just need to optimise the connection orders to keep currents from flowing where they are unwanted while keeping ground resistance minimal. Seems like the same thing here.

[redtails]

A discussion with an engineer is of a lot more value than lone rambling or talking with PR/CEO. That way you can get real insight and talk on the same level

[WolfTronix]

looks like the beads got replaced with 0 ohm jumpers... the beads where isolating the grounds at high frequencies.

[bpa]

Love the sound the little spring makes. *plip*

[uNQuDZ]

@ 10:45, also note the 8-pin SOIC package in the middle has flux residue on top of it. That looks like it has been changed too. And the 0 ohm resistors/jumpers... yeah. The trace on the mA range shouldn't have much influence except maybe for higher creepage distance, i think it's all in the replaced parts.

[voltlog]

the fix might involve some software changes plus some values changed on the passives, adjusting an input filter cutoff freq.. (it does make sense how they changed the ferrite beads and replaced them with 0ohm jumpers to avoid a resonant freq) but like you said Dave, this might be old stock that has been reworked.. the Agilent logo would certainly confirm that.. .anyway nice that they fixed the issue

[symik]

I would like to see it from the view of a Keysight engineer.

[shaman_-]

Another bead or a resistor is now populated near U17.

[TheWP]

Looks like they replaced a few caps with a yellow tantalums. R2 value (bottom left of sideways image) also changed. L1 (near R2) also has a pad next to it. They widened the track by the silkscreen of the revision number. JP4 removed?

[jabelsjabels]

Dang, I'd love to hear how the engineers arrived to that solution!

[PlasmaHH]

What often happens is that the issue gets distributed to different teams, each does whatever they can on it, so software team says "yeah, what we could do is enable the filter per default" and the hardware team does some redesign and in the end both would have done the job, and now you have it extra good.

[OneBiOzZ]

i love the spikes on the old meter when you plugged it in the the new one

[GadgetReviewVideos]

How about C126, can you take a closer look at that and see if that's the same value in both also?

[williamsquires]

Look at the middle left on the PCB - there appears to be some sort of red goop or epoxy resin right above the screw-hole. Also (@ 7:10) follow the screw hole dead North and you'll see a black/dk. gray thing on the original, and on the new one it's silvery. There's also an orange tantalum cap just to the right of it that was black on the old one (rev. 4). Finally, in between those two and lower on the board, there appear to be two SMD inductors that are noticeably bigger on the rev 4 board right near the left edge and NW of the red goop.

[dangerousdave]

Looks like there is also flux residue on those through board joints on the left side (at 18:30)which isn't apparent on the older board. Maybe they replaced those components as well?

[dxdrive]

Does Dave not see the giant track which is changed, which is right under the REV004 / REV006 which he mentioned?

[gatoalfa]

And possibly a firmware change? Can you update the FW on the old one?

[svenk.]

What is the reason for the fertit beads in between the grounds anyway? I See that a lot in datasheets, but from my experience this does more harm than good.
What is your opinion?

[Firecul]

A pad added near L1 on the top left of the board also?

[OneBiOzZ]

also aside from some stop around one of the leads of the inductor, i see no other board changes that hints to me there was 2 revisions of that PCB ...