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

[TomC]

Well I already tried with capacitor replacement and it didn't help. It's not a too great problem for me to replace the IC, if it's suspect. Coil could be a bigger problem. The closest I can find easily available it 100 µH. From TomC's responses, I came to understand that a lower number should be looked upon as a replacement, but the next lowest I can easily find is 10 µH.

AndrejaKo, I think it is possible that you are having trouble with the current sense ending the cycle prematurely, can you check the value of R40, if it's too high I think it could cause a problem similar to this. R40 is the current sense resistor and when the voltage across it reaches 330mV it ends the cycle.

[TomC]

Just thought I could add this info about serial numbers of latest versions: ...............

Thanks for sharing this information!

Since both Owon and the dealer confirm that the 1319xxx serial is the breakpoint for the low noise mods, I think it would be OK, as far as the GND noise is concerned, to buy one of these scopes. If you do, it would be very nice if you can post some images of the GND noise test results on your new scope.

As a point of interest, I wonder if the serial number is based on the Chinese calendar as far as the week of the year is concerned. If that was the case, week 19 would correspond to June 16-22 on our calendar. Again, maybe it's just a coincidence.

[Clint]

If you do, it would be very nice if you can post some images of the GND noise test results on your new scope.

Actually I chickened out and have ordered the Rigol 2072.

As a point of interest, I wonder if the serial number is based on the Chinese calendar as far as the week of the year is concerned. If that was the case, week 19 would correspond to June 16-22 on our calendar. Again, maybe it's just a coincidence.

You know what I was wondering if somehow it could correspond to their tax year or something but I think you are spot on, great thinking !

[Carrington]

Actually I chickened out and have ordered the Rigol 2072.

Very well done. 
I bought my SDS without knowing the noise problem, in fact this became known shortly thereafter.

[lemon]

...
As a point of interest, I wonder if the serial number is based on the Chinese calendar as far as the week of the year is concerned. If that was the case, week 19 would correspond to June 16-22 on our calendar. Again, maybe it's just a coincidence.

From what I saw, the 1st of 2013 was 10 February for China. For example for the serial SDS71021319652 the 19th week is almost at the end of June. But I am afraid that the week in China isn't 7 days period allways...

[TomC]

From what I saw, the 1st of 2013 was 10 February for China. For example for the serial SDS71021319652 the 19th week is almost at the end of June. But I am afraid that the week in China isn't 7 days period allways...

Lemon, here is a link to the calendar I used to come up with the 19th week being equivalent to June 16-22. I went back to the beginning of the year using the blue arrows and counted the weeks. However, I don't really know if that is the way Owon counts the weeks, it's just conjecture!

http://www.prokerala.com/general/calendar/chinesecalendar.php?month=1&year=4711&lang=en

[mlhstock]

As a point of interest, I wonder if the serial number is based on the Chinese calendar as far as the week of the year is concerned. If that was the case, week 19 would correspond to June 16-22 on our calendar. Again, maybe it's just a coincidence.

I doubt that because most Chinese people under 45 don't know much about lunar calendar (Chinese calendar as you quote).

[mlhstock]

Just thought I could add this info about serial numbers of latest versions:

I mailed the supplier on ebay to check I would get a late low noise version and got this reply:

====================
I am sorry but I think this is mistake on EEBLVD, I just checked with manufacturer, our serial # is 1319XXX, it is new version as well ( please e-mail to sales01@owon.com.cn to verify what I am saying if you doubt that ) , 19 not means 19 weeks ( we doubled checked with manufacturer) we warranty you get 2013 June low-noise version ( you can check with manufacturer for the serial #  ), for example the serial# SDS71021319652 or later version.
====================

Based on my experience, Owon and/or their ebay agents don't necessarily tell you the whole truth.

My hypothesis regarding serial number 1319XXX is that Owon might salvage the scopes produced in early 2013 (probably replace with the new version PSU board and add capacitor on adapter board).

For those who know my story, I got full refund from my dealer after I returned the scope to Owon. My dealer didn't refund the customs charge and tax, but they sent me an equal value gift.

[mlhstock]

First sidenote: I have 1303xxx in stock and just as arrived from factory.

Probably a factory refurbished scope.

[TomC]

For those who know my story, I got full refund from my dealer after I returned the scope to Owon. My dealer didn't refund the customs charge and tax, but they sent me an equal value gift.

Glad to hear that!
Did you buy a different scope or are you still looking?

[TomC]

Actually I chickened out and have ordered the Rigol 2072.

Good choice!

From what I've heard it's a pretty solid 70MHz scope with good reviews.

Hope you enjoy your new scope!

[mlhstock]

For those who know my story, I got full refund from my dealer after I returned the scope to Owon. My dealer didn't refund the customs charge and tax, but they sent me an equal value gift.

Glad to hear that!
Did you buy a different scope or are you still looking?

I am still looking. Probably buy a RIGOL.

[AndrejaKo]

Well I already tried with capacitor replacement and it didn't help. It's not a too great problem for me to replace the IC, if it's suspect. Coil could be a bigger problem. The closest I can find easily available it 100 µH. From TomC's responses, I came to understand that a lower number should be looked upon as a replacement, but the next lowest I can easily find is 10 µH.

AndrejaKo, I think it is possible that you are having trouble with the current sense ending the cycle prematurely, can you check the value of R40, if it's too high I think it could cause a problem similar to this. R40 is the current sense resistor and when the voltage across it reaches 330mV it ends the cycle.

I just checked the value using 4-wire measurement system and I got the expected value. My result is 0.269 ohm. I measured directly from one end of the lead to the other end of the lead. It remains stable over time.

[rf-loop]

First sidenote: I have 1303xxx in stock and just as arrived from factory.

Probably a factory refurbished scope.

Arrived from factory stock to my stock March this year!
And these do not have this bad "Noisy GND issue", they are just normal working units.
And here and there have seen test made with these.

clarify: "just as arrived from..."  (means factory original condition)

[Carrington]

The next cheapest that I found, but is glass:
http://www.ebay.es/itm/380691935873

[TomC]

I just checked the value using 4-wire measurement system and I got the expected value. My result is 0.269 ohm. I measured directly from one end of the lead to the other end of the lead. It remains stable over time.

That eliminates R40, unless it's intermittent or cold solder joint. To me, this seems to point to the IC's internal circuit, like something wrong with the internal threshold voltages. If you want to get more evidence before replacing the IC, you could try a 1 ohm resistor in parallel with R40, that'll give you a total value of about 0.21 ohms. If this improves the situation, maybe only with battery operation where the input voltage is below 8.4V, it'll point to the current sense threshold inside the IC as being the culprit.

Of course other components are also suspect, for example the coil, but from my experience, coils seldom fail, so something as a short in the winding is less likely, nevertheless possible.

[AndrejaKo]

The half-level  points are still there with an ON Semi MC 34063A, but are now a bit different. Now every square starts with at least one pause near the mid level. Sometimes, there are more of those pauses. The difference is that they are usually very, very short, only few tens of nanoseconds in length. There are several types of bad ones, though.

The most common type of square wave is the fast 2 level one. After probing for a while, I'd say that they're more than 90% of captured squares. The is some variation of time it takes to jump from the first voltage level to the second, but it's usually very short.

There are also two more types of square waves I've seen. There's the fast 3 level one. First level dwell time of always very short. There's also a 2 level slow square. It seems to be a bit more common than the 3 level one, but it's still quite rare.

I forgot to show a picture of duty cycle now. It's now mostly around 50%, but goes as low as 40% sometimes and as high as 60% sometimes. At low timebase, the waveform looks healthy.

Also it seems that I forgot to mention the main issue! The large noise peaks are still there. They are not synchronized to any particular point on the MC's cycle. I believe that the noise is just riding on top of the signal MC is creating. The signal on pin 2 of the MC is clean, because I desoldered SMD capacitors I added which connected the MC's power pin to a piece of non soldermasked ground. It seems that somehow the peaks were entering in the MC through them. I added them back for experimental purposes and the peaks on the pin 2 appeared again. Now that I removed them, the peaks on pin 2 are gone too.

The peaks are still the strongest between the TL431 and the "R40" resistor which are almost touching on my PSU. It's also strong near the two 470 µF capacitors marked EC8 and EC5 on my board that are close to 1000 µF electrolytic and L1 coil and  in the area near the LM324L.  Since this scoping was done on battery power, the area south of the transformer was quiet, as expected.

[TomC]

The half-level  points are still there with an ON Semi MC 34063A, but are now a bit different. Now every square starts with at least one pause near the mid level. Sometimes, there are more of those pauses. The difference is that they are usually very, very short, only few tens of nanoseconds in length. There are several types of bad ones, though.

The most common type of square wave is the fast 2 level one. After probing for a while, I'd say that they're more than 90% of captured squares. The is some variation of time it takes to jump from the first voltage level to the second, but it's usually very short.

There are also two more types of square waves I've seen. There's the fast 3 level one. First level dwell time of always very short. There's also a 2 level slow square. It seems to be a bit more common than the 3 level one, but it's still quite rare.

AndrejaKo, my first impression is that these are much better than what you had before, I don't think these pauses are any longer due to a problem with current sense, they may be more related to the switching characteristic of the output Darlington and stray capacitance. How is the overall cycle, is it anything like what you had before or closer to the image that rf-loop posted? Did you have any improvement on the large noise spikes? Can you post some images of both of these.

[Carrington]

Wow... At the rate that this topic is going, soon will be the winner! 116 and up.
And 200760 Views! I believe that the people enjoy reading about the misfortunes of others... As with a TV serial. 


Do not get me wrong, is only a funny note. Until a few pages everyone was very happy with their SDS.

[AndrejaKo]

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.

[Carrington]

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.

You'll have to apply the divide and conquer technique. Have you tried to to make it work only with batteries? Completely removing the PSU and them then the DC/DC adaptor board, except the driver for the screen. But don't forget that the main board has other DC/DC converter, one power directly the entire DAC, digital and analog sections.

Sorry then not them!

[AndrejaKo]

I'm not sure I understand what you're saying...

Do you want me to try to run the DAC board by using only an external power supply?

Right now, I only have one good  linear "lab" power supply, with only one channel, so it will take me a while to make a PSU for -7.6 V and then to rig everything up so that it starts.

I was thinking about doing things the other way around and start by running the PSU with a dummy load and then probe with another scope (when I manage to arrange access to it), since that to me seems easier to do. I'm pretty sure that the noise source is in the PSU itself. Few pages ago, I tried out the PSU with adapter power cable disconnected and probed the -7.6 V with my soundcard. I still had the noise peaks with same frequency as the ones I'm seeing on the scope GND.

[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?

[Carrington]

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

[Carrington]

I'm not sure I understand what you're saying...

Do you want me to try to run the DAC board by using only an external power supply?

Right now, I only have one good  linear "lab" power supply, with only one channel, so it will take me a while to make a PSU for -7.6 V and then to rig everything up so that it starts.

I was thinking about doing things the other way around and start by running the PSU with a dummy load and then probe with another scope (when I manage to arrange access to it), since that to me seems easier to do. I'm pretty sure that the noise source is in the PSU itself. Few pages ago, I tried out the PSU with adapter power cable disconnected and probed the -7.6 V with my soundcard. I still had the noise peaks with same frequency as the ones I'm seeing on the scope GND.

One good linear "lab" power supply, help. You can buy also fat batteries. -> ~ -7.6V