REVIEW - Owon SDS7102 - A look at the SDS series from Owon

[lemon]

Unfortunately, I haven't functional my scope. Pehaps some measurement to my circuit will help you.
Still, I am wait the AOZ1094 to arrived.

Carrington, the EMI shielding where you thinking to apply? Front or back of the screen and what dimensions we are need?

From, is as glass, but with a conductive coating.
https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg279474/#msg279474

I see, you are thinking to use it like a glass in front of tft display. I saw that you have done the same question to the Rigol DS2072 thread.
I''ll doing a search about this.

By the way, can someone to take a capture how display the scope a 40mVpp 100kHz sine wave at 1ms/div 10mV/div or 5mV/div?  One channel and 10M memory depth. Please with scope with not gnd noise. Is there any aliasing?

[Carrington]

I see, you are thinking to use it like a glass in front of tft display. I saw that you have done the same question to the Rigol DS2072 thread.
I''ll doing a search about this.

That's right, but the conductive surface should be behind. And it can be checked only if someone have this side accessible, not my case. Although I think that it is a simple plastic.

https://www.eevblog.com/forum/testgear/first-impressions-and-review-of-the-rigol-ds2072-ds2000-series-dso/1650/
The second image was obtained from this video:
http://www.eevblog.com/2012/09/26/eevblog-360-rigol-ds2000-oscilloscope-teardown/

[TomC]

Hi TomC!

I forgot to show the general duty cycle and to write about the large peaks in the last post, so I updated it. Basically, the peaks are still there and they don't seem to be related to MC's operation. Could the TL431 be producing them somehow?  Duty-cycle is close to rf-loop's.

AndrejaKo, looking at the captures on your updated post I notice there is a shift in frequency between them. You had the scope stopped when you made the capture, so I'm wondering if the shift is gradual or do you see a lot of jitter when looking at it dynamically?

It's difficult for me to imagine a scenario where the TL431 may be causing the noise, but anything is possible. However, I have to first suspect the -7.6V where there is a lot more dynamic activity going on. I looked at a PSU circuit board side picture you previously posted and added some notes, see attachment. It's possible that the noise you see around EC5 & EC8 is passed on from the MC area because of where the ground trace narrows next to R40 and the TL431. At some point when you have resolved this problem it may be a good idea to use a larger conductor there to improve GND noise in general. For now, I think that the source of the noise is in the MC area, possibly R40, or some other component. There is not very many and you already replaced the MC IC itself. If you have a resistor similar to R40 I would try replacing that next.

[AndrejaKo]

I'm re-posting an animation I made few pages ago right now. It's purpose was to show how the frequency shifts look like. Basically there's around 20 ms between peaks, but they keep jumping around in the region of approximately 2 ms from the 20 ms point where I'd expect them.  It's not all that visible on the animation, but peaks jump both to the left and to the right. Other than that, the animation faithfully shows what's happening on the screen of the oscilloscope and the peaks are jittery.

As for resistor replacement, most of the resistors of correct nominal value I can find easily are inductive, ceramic wire wound and I suspect that they would not be suitable. I could go for series combination of 3 resistors each marked 0.1 ohm, but that would exceed the value I need.  Maybe 3 metal-film resistors in parallel, each with nominal value of 1.8 ohm? That would be pretty close. OK, I'm obviously too tired to calculate...

[TomC]

Maybe 3 metal-film resistors in parallel, each with nominal value of 1.8 ohm? That would be pretty close. OK, I'm obviously too tired to calculate...

OK AndrejaKo, take a rest and will try again later (tomorrow). You'll need, seven 1.8 ohm in parallel (0.257 ohms) to come close to the value.

Edit:
When I mentioned frequency shift in my previous post, I meant the signal where you show the duty cycle, not the big noise spikes. Although the duty cycle looks a lot closer to the one rf-loop posted, I was wondering if there was jitter or a gradual change in frequency. On the first duty cycle capture I see a range from 43-50KHz, on the last capture I see a frequency below 38KHz. Also as you pointed out the duty cycle varies quite a bit.

If everything is working correctly and the converter is working in CCM the duty cycle is a function of the voltage in and voltage out approximately like this: DC = Vout / (Vin + Vout)   If you work that out with Vin = 8.4V it comes out pretty close to 50%. Of course when you are using the battery it'll change some. But it shouldn't be changing back and forth from 40% to 60% as you reported.

The frequency is controlled by C6 which is charged and discharged by an internal current source and sink. The current values are fixed so the voltages in and out of the IC shouldn't affect the frequency. However, the charge current is increased to cause a short oscillator cycle if too much current is detected by the current sense circuit (which checks the voltage across R40). So if everything is working correctly the frequency should be pretty steady, going back and forth from 38KHz to 50KHz doesn't seem right to me.

In conclusion, I think something is still wrong. You replaced the IC and things got better, maybe because of slight differences in characteristics between the two ICs, but still there seems to be an underlying problem. If that gets fixed, maybe the old IC will also work correctly. Like I said before, there is only a handful of external components, and I think I would start with R40.

Note: The ON Semi application note for this IC states that you can disable the current sense circuit by connecting pin 7 to VCC. So for a test, it may be OK to short R40. I wouldn't do it for too long and would be watching for other components overheating. Up to you, if you want to risk it!

[TomC]

By the way, can someone to take a capture how display the scope a 40mVpp 100kHz sine wave at 1ms/div 10mV/div or 5mV/div?  One channel and 10M memory depth. Please with scope with not gnd noise. Is there any aliasing?

Here are some captures, I hope you don't consider my scope noisy
There is of course no aliasing at 1ms/div with 10M memory depth. I had to set the time base to 2s before I saw any aliasing.

Edit:
I made a big boo-boo when I captured these images. I connected the probe to the generator's ground, and the scope's ground lead to the generator's output. Miraculously I got something resembling a signal. Actually, when I first looked at it I saw big noise spikes, not quite as bad as AndrejaKo's but similar looking. Not yet realizing I had reversed the polarity I did a self calibration. After that the signals  looked better so I captured the images and posted them. So I'm leaving them here as an example of what you get if you make this mistake. I'll post properly captured images in a separate post.

[TomC]

By the way, can someone to take a capture how display the scope a 40mVpp 100kHz sine wave at 1ms/div 10mV/div or 5mV/div?  One channel and 10M memory depth. Please with scope with not gnd noise. Is there any aliasing?

Here are the captures done correctly this time. There is no aliasing at 1ms/div with 10M memory depth and I still had to set the time base to 2s before I saw any aliasing.

[lemon]

TomC many thanks for the captures.
When I saw your first captures, freak! The last ones is clearly without any alliases (and with triggering appearing right).
It is mine missing about how to connect with generator, probe or bnc-bnc (50 Ohm). Probably the true is bnc to bnc but author doesn't say...
The whole story held to Rigol DS2072 thread that one member (Galaxyrise) ask the rest member how is it to the other scopes becouse the Rigol High-Res mode is so different from what his expected.

Then his demonstrate two captures with the same conditions like ask you, but I can't undestood why displaying that! I don't meaning about aliasing (it is there and the wave isn't stable) but with 10mV/div, it must to cover 4 div. I haven't experience about Rigol menu, but here something goes wrong. Maybe Carrington that has Rigol explaining that.




After some messages another member (Hydrawerk) demonstrate the Agilent DSO-X-2002A results that is fine and clearly, but at two captures with different mem. depth doesn't capture the triggering right to one of them (remember TomC what told about this...). At this measurement the connection btw generator and scope is internall because has internal generator option.

[AndrejaKo]

First one thing I've noticed: With new regulator, both regulator and coil run much cooler than before. Previously I couldn't hold my finger next to them because of heat. Now they're just very hot, but not burning hot.

I did some scoping on the timing capacitor itself and its waveform is very noisy and jittery. According to the scope's frequency measurement, the frequency is always changing. It's usually around 48 kHz, but can go as high as 60 kHz sometimes.  I'm attaching image with infinite persistence. Another image which I found interesting is when I probes the pin 2 and pin 3 at the same time. It seems that there are huge bursts of noise on pin 3 when pin 2 is high.


Should I try changing the capacitor? It seems like a polyester capacitor to me, but from what I heard they should be pretty good.

 I can easily obtain ceramic multilayer capacitors of same capacitance and tolerance with NP0 dielectric and try with them, to see if it's the capacitor.

[Carrington]

The whole story held to Rigol DS2072 thread that one member (Galaxyrise) ask the rest member how is it to the other scopes becouse the Rigol High-Res mode is so different from what his expected.
...

As I have understood, it occurs only in the HighRes mode, is more than evident. I suppose that it's a bug in the firmware, but I have no idea why it happens.

[lemon]

@ AndrejaKo = I see a very well square at pin2, probably it is better than rf-loop.
I think that if I could to measure this point I hadn't better result.

@ Carrington = It is strange for me, not how this appears (about aliases or not stability in vertical axes) but why it hasn't four divisions at the Vertical axes.
At the first capture the Resolution is at the Auto and probalbly the Rigol set to maximum resolution but at the second capture the resolution set to lower 14kPoints about and the Vertical is only 1 div...10mV...why?
This is fw bug, sure.
Can you upload a capture with the same condition and another with some other resolution that dissapearing this phenomenon (of course at 40mV signal)?

[Carrington]

Hi lemon!
Someday I'll post a picture of my "lab" and you'll see that I have not much instrumentación. Not long ago I just had a simple multimeter. In this forum there are people who can afford (for whatever reasons) a lot of instrumentation, not my case. In this world everything is very badly distributed, and I have no hope that this will change.

Anyway, to this I need a signal generator, but I have not one. I'm thinking about where I can get a similar signal, and the only thing that comes to my mind now is ~20KHz of sound card.

[lemon]

Don't worry about this, Carrington.
I'll do the same question to the Rigol thread.

TomC, sorry for this adding effort but at the first yours capture "1ms-Div.png" the sampling is 500MS not 1GS.
Can you see what it is happening? I want to upload this capture to the thread of Rigol.

[TomC]

TomC, sorry for this adding effort but at the first yours capture "1ms-Div.png" the sampling is 500MS not 1GS.
Can you see what it is happening? I want to upload this capture to the thread of Rigol.

Lemon, I'm a retired man, I love playing with this stuff. Sometimes I have to help the wife with house shores, too keep her happy, but other than that I'm with the computers and the electronics.

What you see in the captures is normal for the SDS7102, as you use a slower time base, at some point (1ms/Div) the length of time that you are capturing doesn't fit in the memory (10M) at the maximum sampling rate (1GS) and the scope automatically lowers the sampling rate (500MS, etc.).

The confusing part about it is that when you stop the scope and look at the stored waveform, if you change the time base the sampling rate displayed changes as described above. But you are not capturing anything new, so the sampling rate can't possibly increase in reality. It's just the way the firmware implements it, it just looks at the current time base setting and the memory length and from that decides what sampling rate to display.

[TomC]

First one thing I've noticed: With new regulator, both regulator and coil run much cooler than before. Previously I couldn't hold my finger next to them because of heat. Now they're just very hot, but not burning hot.

I did some scoping on the timing capacitor itself and its waveform is very noisy and jittery. According to the scope's frequency measurement, the frequency is always changing. It's usually around 48 kHz, but can go as high as 60 kHz sometimes.  I'm attaching image with infinite persistence. Another image which I found interesting is when I probes the pin 2 and pin 3 at the same time. It seems that there are huge bursts of noise on pin 3 when pin 2 is high.


Should I try changing the capacitor? It seems like a polyester capacitor to me, but from what I heard they should be pretty good.

 I can easily obtain ceramic multilayer capacitors of same capacitance and tolerance with NP0 dielectric and try with them, to see if it's the capacitor.

AndrejaKo, I need to look at these waveforms in more detail, they seem very interesting. Right now I have to run a 2 or 3 hour errand, but I'll give you more feedback when I come back. If you have a similar capacitor go ahead and change it, it'll be one less component to worry about. The capacitor's you propose should be good enough at least for a test.

[lemon]

TomC very informative as always, thanks.

[AndrejaKo]

AndrejaKo, I need to look at these waveforms in more detail, they seem very interesting. Right now I have to run a 2 or 3 hour errand, but I'll give you more feedback when I come back. If you have a similar capacitor go ahead and change it, it'll be one less component to worry about. The capacitor's you propose should be good enough at least for a test.

I changed the timing capacitor and there's more or less no difference, so I think that we can safely rule it out as the source of the problem.

[Carrington]

I changed the timing capacitor and there's more or less no difference, so I think that we can safely rule it out as the source of the problem.

Disconnect the circuit that generates the -7.6v, now use five 1.5v batt. in series or your linear PSU (better batt.), connecting the negative terminal to -7.6v point and the positive terminal to gnd, now turn on the oscilloscope using only your lithium battery. Continue appear those spikes?

Note: If you use your PSU don't dare to power it using the network (220V).

Do not worry, the oscilloscope "up" successfully even without the -7.6V. Although as is logical the input stage will not respond properly.
It not will be destroyed, I made the test on mine. Note that the -7.6v only power to the analog input stage through a LDO (7905).

[AndrejaKo]

I changed the timing capacitor and there's more or less no difference, so I think that we can safely rule it out as the source of the problem.

Disconnect the circuit that generates the -7.6v, now use five 1.5v batt. in series or your linear PSU (better batt.), connecting the negative terminal to -7.6v point and the positive terminal to gnd, now turn on the oscilloscope using only your lithium battery. Continue appear those spikes?

Note: If you use your PSU don't dare to power it using the network (220V).

Do not worry, the oscilloscope "up" successfully even without the -7.6V. Although as is logical the input stage will not respond properly.
It not will be destroyed, I made the test on mine. Note that the -7.6v only power to the analog input stage through a LDO (7905).

I'll try that and report back the results.

[AndrejaKo]

I got another lithium battery and connected it to the negative voltage terminal with the MC34063A removed and I got some extremely interesting results! All probing was done with a 150 MHz probe.

First, my conclusion is that those peaks which always occurred at around 20 ms seem to be under influence of at least two sources, one inside the scope and one on the outside!

I came to that conclusion when I noticed that the peaks seem to disappear for a short while when I was probing GND. After taking a look, it seems that they come in 600 ms bursts with 800 ms of pause between them. Inside of the burst the peaks occur at every 20 ms. They are illustrated in the first four attached images.

After moving the scope to my no electronics room, the large peaks disappeared.  Now to refresh readers' memory, with the MC running and the scope in my no electronics room, I still had the peaks, so at least some of those peaks had to be coming from somewhere near the MC.

Anyway, in the no electronics room, I only got the smaller peaks I mentioned few times before. My guess is that they would be coming from the adapter board itself. They are illustrated in the last two images.

I also replaced PSU screws with higher quality ones an would recommend this small "upgrade" to anyone else who want to spend some time experimenting with this scope.

[Carrington]

AndrejaKo: Have you twisted the power cables (-7.6v)? And are they as short as possible?

After moving the scope to my no electronics room, the large peaks disappeared.  Now to refresh readers' memory, with the MC running and the scope in my no electronics room, I still had the peaks, so at least some of those peaks had to be coming from somewhere near the MC.

Have you done the test without the MC in the "no electronics room"?

Anyway, in the no electronics room, I only got the smaller peaks I mentioned few times before. My guess is that they would be coming from the adapter board itself. They are illustrated in the last two images.

Well now I'm pretty sure that this noise comes from the adapter board. Please, show me a picture of this board.

[TomC]

After moving the scope to my no electronics room, the large peaks disappeared.  Now to refresh readers' memory, with the MC running and the scope in my no electronics room, I still had the peaks, so at least some of those peaks had to be coming from somewhere near the MC.

Very good!
I think you are making considerable progress in unraveling this mystery!
Trying with batteries as Carrington suggested was a good fault isolation strategy that paid off!

I agree with your conclusion that this noise is very likely originating from more than one source. I would recommend that from now on any further tests be conducted in the no electronics room.

I think the next step is to re-install the MC IC and see if any of the high voltage spikes are still present, of course you must do this test in the no electronics room.

If the high voltage spikes are gone, perhaps you can shift the focus to cleaning up the remaining lower level noise.

You may also try to isolate the source of the high voltage spikes in the areas of the building where electronics are present. Part of this noise is probably conductive, and may be reaching the scope via the power plug, for that part you can try ferrites on the power cord. However, it appears that the bulk of it is radiated, since you have reported it while running the scope from the battery. That is more difficult to eradicate. First I would check for high voltage spikes with no probes attached to the BNC's, you may also want to try with 50 ohm terminators, both plugged in all the way and just acting as a shield cap with the center conductor not making contact. If there is little or no noise with these setups, is likely that the bulk of the high voltage spikes are making their way into the scope input via the probe cables. I think that's the more likely scenario, if it isn't, some of the EMI shielding products that Carrington is looking into to keep the scope from radiating EMI should be also as effective to keep external radiation from entering the scope.

My electronics lab is also my computer room, needless to say that there is often undesirable EMI radiation from multiple sources. These wasn't an issue with my 60MHz CROs, if I saw anything it was usually so faint that it was easily disregarded. With the 150MHz+ DSO is a different story. So to stop hunting ghosts I've been keeping ferrites on each end of my probe cables. I've found that the larger ferrites intended for power cables work the best because there is enough room to loop the probe cable an extra turn to double the inductance. So you can try and see if a setup like this helps with the high voltage noise spikes caused by your electronics.

[Carrington]

I agree with your conclusion that this noise is very likely originating from more than one source. I would recommend that from now on any further tests be conducted in the no electronics room.

Yes, please make all tests in the "no electronics room".

[AndrejaKo]

@Carrington Yes, the test without the MC was done in the no electronics room. In future, I'll do all tests there. The adapter board is the standard 3.0 version board. So far, I did not make any modifications to the board itself, other than attaching ferrites to the cables. Also thanks for the encouragement to test this with batteries only. I needed it.

@TomC I'll get some ferrites for power cables and see if they help when running from AC.  I'll report back when I'm finished testing with MC34063A reinserted.

[Carrington]

@Carrington Yes, the test without the MC was done in the no electronics room. In future, I'll do all tests there. The adapter board is the standard 3.0 version board. So far, I did not make any modifications to the board itself, other than attaching ferrites to the cables. Also thanks for the encouragement to test this with batteries only. I needed it.

Oh no the 3.0! Then most of this noise (of the attached image, ) comes only from the adapter board.
Now you know for sure that most of the "big noise" comes from the circuit associated with the MC.
Because this attached image is without the MC and in the "no electronics room", right?

Sorry, I made a little mess.