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    #41
    Re: Let's teach Keri how to use an Oscilloscope!

    I feel that maybe the low power of this PSU minimized the spikes, or maybe it runs stuff at different frequencies?
    but in the first post you said
    Oddly, a really cheap 6 year old pull from an upgrade that weighs about ONE pound came up relatively clean with no motherboard attached, but started spiking all over just like a new Antec EA380 when attached to a motherboard.
    so overall it seems to me mobo is the common factor here.
    (bad psu perhaps works on lower freequency and is of lower power, BUT that would make ripple more visible...also it's crappy design and caps...)

    i would rather use some other load, and then crank up the 'vertical zoom' on the scope(so you can see real small voltage fluctuations).
    hell perhaps even just few hdds attached to few molex plugs of the psu.
    that should at least give you some idea....(offcourse, if you don't have hdds handy don't buy them just for this)

    i should think of something readilly available that can be used to load the psu to at least 200-300w...
    i better do some ohm law math and see if i have the resistance i need in any of handy devices...
    no, not 12v bulbs, it takes too many of them...

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      #42
      Re: Let's teach Keri how to use an Oscilloscope!

      Hello.

      I found yet another test subject.

      The Seasonic S12-600 in my video editing PC (retired in favor of a Mac Pro)

      At idle with no load, the S12 has a fairly clean ground and spiking like the other two noisy PSUs on the 5v and 12v - when measured with a standard probe. Measuring with the capped probe eliminates the spikes.

      The only major difference is the relatively clean ground signal.

      Upon opening for inspection and cleaning, I found that the S12 has a bunch of very tightly packed NCC KZE and KY caps on the secondary all in apparently good condition..

      More data! Arrrgh! At least I got some good tips on scope settings.


      Just beginning to learn about this scope business,
      Keri

      Head Hurtz
      Last edited by KeriJane; 01-01-2009, 10:55 PM.
      The More You Learn The Less You Know!

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        #43
        Re: Let's teach Keri how to use an Oscilloscope!

        Been away.
        And i4004. I think I had a drink, oh, 4 or 5 months ago.
        Didn't even spike the eggnog this year.

        Scope trace is probe's tip referenced to scope's/probe's ground.
        If ground loop makes scopes ground potential jump around then trace will too.

        I think i4004 mentioned the problems with current in the shielding already.
        [I read through fast playing catch-up.]
        Remember the coax used for scope probe wire is essentially antenna wire.

        If you run a wire direct from building/earth ground to a common ground on mobo then you can eliminate ground continuity (bad connection) problems in PSU and connectors from affecting the trace.
        - In other words shunt across any bad ground connections in PSU.
        This way you are putting mobo's ground at earth ground which is the same as the scopes earth ground.

        That only fixes one of the possible problems though.
        - Bad ground continuity through PSU.

        -

        You can also (with probe's ground disconnected) put probe's tip on mobo's ground to directly measure any noise referenced to earth/scope ground.
        Mann-Made Global Warming.
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          #44
          Re: Let's teach Keri how to use an Oscilloscope!

          Scope trace is probe's tip referenced to scope's/probe's ground.
          If ground loop makes scopes ground potential jump around then trace will too.
          yes, but it should be 60hz frequency with harmonics, as that's the characteristic of the loop.
          it starts with the mains...
          then junk is imposed on it.

          I think I had a drink, oh, 4 or 5 months ago.
          i have a beer..perhaps once or twice a month, if that.
          it seems to be beer is becoming piss these days...
          can't find good beer, can't find good olive oil...fuck it...

          i'll see if i can find those caps to put on the probe...i have few psus and mobo handy...although my interest in doing it is rather low...
          as i know good psus have low ripple and that's mostly enough for me.
          (but keri got me curious)

          Comment


            #45
            Re: Let's teach Keri how to use an Oscilloscope!

            >>>>
            yes, but it should be 60hz frequency with harmonics, as that's the characteristic of the loop.
            it starts with the mains...
            then junk is imposed on it.
            <<<<

            I was just stating 'how' unstable ground affects image on scope.
            Comment generic in regards to how the ground got unstable.

            >>>> Drinkin'
            I was just poking back at the "are you drunk" tease.
            I've never like beer since I got shit-faced on it when I was 10.
            Dad had a wet bar downstairs.
            Do like various whiskeys, mixed drinks, margaritas.
            For whatever reason about my early 30's I just quit drinking except at sometimes nice restaurants. Nothing against it, just the thought doesn't occur anymore.

            .
            Mann-Made Global Warming.
            - We should be more concerned about the Intellectual Climate.

            -
            Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

            - Dr Seuss
            -
            You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
            -

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              #46
              Re: Let's teach Keri how to use an Oscilloscope!

              KeriJane:

              Did you ever resolve your Oscope noise questions?
              Is your Owon by any chance a model EDU5022 ?
              Have you tried measuring your PSU unit without those added capacitors stuck on the probe tip, but using the "math mode" of the Owon set to " CH1 minus CH2 " ? This may work better without ground clips, using CH1 probe tip to PSU measure point, and CH2 probe tip to PSU black ground line in DC connector, [using CH1 trigger setting ] If not so good, then also attach CH1 ground clip to PSU black ground line in DC connector. Depending on the configuration of the vertical input amp circuit in the Owon, you may need to also attach CH2 ground clip to the same black PSU ground line. Also, you can try different trigger menu coupling options [High frequency reject and/or Low frequency reject].

              Putting those 2 capacitors on the input of the probe just causes a severe bandwidth limiting to occur ["shorts out" a significant portion of the signals you are trying to view ]. This will give you a cleaner looking but attenuated signal; however, it will not be a true representation of what is actually at the point you are trying to view.

              Huck

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                #47
                Re: Let's teach Keri how to use an Oscilloscope!

                Hi Huckfinn!

                Thank you for the great advice on Math mode.

                It is an Owon PDS5022S scope. I'm not sure how that differs from an EDU. I found a picture of an EDU5022 and it looks nearly identical to mine.

                The Math function has me confused. I put the two probes on and it gives me the differential value as a green trace (Ch,1 & 2 are red and yellow). But..... I don't see how to reference the green trace to anything. Adjusting the v/div on both channels seems to affect it but I'm not sure exactly what I'm looking at.

                I haven't yet tried Math + ground clips. I still haven't used High/Low frequency reject. I did find trigger menu - AC/DC coupling, HF and LF reject, but I'm not sure how to use it. The default appears to be AC coupling.

                Yes, I realize that the decoupling caps distort and/or attenuate the signal. But the people that recommend it say that it is recommended by the ATX spec for measuring purposes. Also, I've read that the ATX spec specifies that a Differential Probe be used. I think that maybe one wouldn't put Decoupling Caps on a differential probe.
                Does the Math function give me a Differential Probe on the cheap?

                Speaking of probes, what would you think of an "Active" Probe? Isn't that the one that has the sensing element right near the probe tip? Like a Differential probe?

                I bought an older New In Box 300w Enhance PSU on sale just for maybe fixing the next ancient system that might stroll in. The PSU is well made but with cheap Teapo and Su'scon caps. However, like my other old "test" PSUs
                lying around, it doesn't generate the big spikes that I see on my more modern ATX 2.0 PSUs.
                The scope appears to work as one would expect on these older, less powerful units without the Decoupling caps.

                I've been a bit busy lately and sick too. But I'm feeling better now and will maybe learn some more soon.

                One thing in particular has me perplexed: The measured P2P voltage changes with the v/div setting! I understand that the v/div setting alters the size on the screen, but I would have thought that the Measurements reading would be independent of the screen display.

                Have Fun,
                Keri
                Last edited by KeriJane; 01-22-2009, 08:04 PM.
                The More You Learn The Less You Know!

                Comment


                  #48
                  Re: Let's teach Keri how to use an Oscilloscope!

                  PDS5022S and EDU5022 look to be the same except PDS5022S has RS232 and USB ports.
                  EDU5022 has USB port only.

                  I don't think RS232 matters to most people anyway.
                  Mann-Made Global Warming.
                  - We should be more concerned about the Intellectual Climate.

                  -
                  Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

                  - Dr Seuss
                  -
                  You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                  -

                  Comment


                    #49
                    Re: Let's teach Keri how to use an Oscilloscope!

                    Hi again KeriJane:
                    When you use the "math" function on the Owon, it is the equivalent of choosing "add" CH1 plus CH2 with CH2 inverted an an older style scope. Your Owon does this by directly subtracting the CH2 signal from the CH1 signal, therefore displaying the "difference" between the two, giving you the "differential" display. Since your scope is a two channel scope you do not need to purchase an active special purpose expensive differential probe, because you can make most of these differential measurements with your Owon using "math" mode and the two channels. Active probes are also special purpose expensive items that are designed primarily to give even more isolation of the circuit under measurement from the input circuit of the Owon, but since the Owon has an input impedance [AC resistance] of 1 Meg Ohms [10 Meg Ohms with a 10X probe or 10X probe setting]; an active probe is not necessary for the vast majority of measurements that you will want to make, unless you get involved in working with some very sophisticated circuitry. A PSU circuit will not be disturbed by having a scope hooked to it that has such a relatively high input impedance.

                    When the signal you are looking at appears to change in absolute value with a change in vertical scope gain, and you know the signal itself is not changing, it is usually due to one of two factors. In single channel mode, this phenomena is usually due to a ground reference problem. In dual channel differential mode, the problem is usually due to not having both channels on the same vertical gain setting.[and/or not having both probes at the same attenuation setting if they are switchable]. Ground reference problems can also cause differential measurements to appear illogical. You are correct in stating that the absolute values of circuit displays should not be changing with a change in vertical gain settings. [the displayed height of the waveform will of course change with different gain settings].

                    I am glad to find out that you are feeling better.

                    Huck

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                      #50
                      Re: Let's teach Keri how to use an Oscilloscope!

                      KeriJane:

                      I also wanted to mention that if you choose to set the probe switch of your Owon to the 1X setting [10X is normal], then the Owon will limit the bandwidth of the vertical amplifiers and following processing circuitry to 5 Mhz. To get the full 25 Mhz performance from the scope, both probes need to be set at the 10X setting of the small switch on the probe body. This is the preferred setting anyway, to get maximum scope-from-circuit isolation. You would only use the 1X setting when looking at lower bandwidth signals that are low enough in amplitude that even your highest vertical gain settings are not quite enough to adequately view the signal.

                      Huck

                      Comment


                        #51
                        Re: Let's teach Keri how to use an Oscilloscope!

                        I'd resurrect this thread for a while since lately I am being bothered with the same.

                        First to say, I should not be seing any ground loop as both scope and PSU are on the same extender.

                        Second thing is, I am seeing the same ripple when I connect grounding of the probe to PSU's ground AND the probe tip to the same ground. BUT I do not see significant ripple on all PSUs. Only on those with high ripple being measured than on the voltage side. On these PSUs, also the ripple changes while taking readings from different places.

                        So the matter is this. Is it problem with by measuring method somewhere? Or is it actually OK, because the problem is on the PSU side (not grounded properly, bad driver, bad output filter)?
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                          #52
                          Re: Let's teach Keri how to use an Oscilloscope!

                          Put the scope ground lead which has the alliagator clip at the end attach that to the tip of the scope probe, now you will have a little loop, move that around the power supply board and see if you see any high frequency ripple showing on the screen.
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                            #53
                            Re: Let's teach Keri how to use an Oscilloscope!

                            K, basically testing it like antena? Well having this not connected together, I remember there is really small ripple (some 4 mV top) so definitelly it is not measuring bullshit Will check next time havign connected.

                            As I have stated in other tread anyway, ripple is supposedly to be measured very near or directly accros the decoupling capacitors. I have tried this for the +5 V SB last time and the PSU was out of spec anyway (by some incredible numbers), so I am pretty sure the other rails are the same and it really has bad ripple controll on it's own, even though I may have not measured it that accurately.

                            Also it is very long time on the market (OCZ ModXSream) and in some reviews I have seen it going over ATX spec even brand new. Not sure how long this particular one stayed on shelf, but has Teapo, could dry out partially…
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                              #54
                              Re: Let's teach Keri how to use an Oscilloscope!

                              Also, turn on the bandwidth limiter; ripple really isn't found above about 100kHz, so if you can limit it that much, that works well. A small RC filter (with AC-coupling to 1 Hz) could work.
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                                #55
                                Re: Let's teach Keri how to use an Oscilloscope!

                                Yeah I got the integrated one over 20 MHz turned on. It seems to be some industry standard of maximum frequency over long time so it became a norm even after that, also the Intel white paper states to use 20 MHz.
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                                  #56
                                  Re: Let's teach Keri how to use an Oscilloscope!

                                  .
                                  Last edited by MDOC; 01-24-2013, 07:41 AM.

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                                    #57
                                    Re: Let's teach Keri how to use an Oscilloscope!

                                    Originally posted by MDOC View Post
                                    .
                                    Want that (and this) post deleted?
                                    sigpic

                                    (Insert witty quote here)

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                                      #58
                                      Re: Let's teach Keri how to use an Oscilloscope!

                                      Originally posted by ratdude747 View Post
                                      Want that (and this) post deleted?
                                      Yes, please. It's a mistake. Thanks.

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                                        #59
                                        Re: Let's teach Keri how to use an Oscilloscope!

                                        Originally posted by budm View Post
                                        Put the scope ground lead which has the alliagator clip at the end attach that to the tip of the scope probe, now you will have a little loop, move that around the power supply board and see if you see any high frequency ripple showing on the screen.
                                        OK, did testing of two server 1U PSUs yesterday (one more to go today). Waving with the loop over PSU loader resulted in ripple going from <<1 mV to some ~2-3 mV, that is OK I think?

                                        Anyway, the best supply of those three, a resonant one, man, that ripple, you want to have it. Worst ripple was with 2 A only at +12 V rail (just cooling fans) of 23,4 mV due to different type of switching on light loads. It switched to better driving over 20 % load and achieved 12 mV ripple at 100 %! That's 200W 80+ Gold certified unit.

                                        The other supply, oldest and somewhat cheaper built 3Y/FSP one, was still well within spec with 55,6 mV top @+12 V. So I think those previous units really "just" had poor ground and/or switcher driving.
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