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

[lemon]

I done one measurement of 10MHz at 40mV output. Two large ferrites with each of them with one looped cable inside.
Yes there is an improvement but without right triggering. The reason of this is that I have removed all the mods to the Led Back-light Circuit and for this time the gnd-noise has increased.

Nice!
I think it will get even better when you put the mods back in.

At the end of this investigation...I''ll come back with this. 

[Hydrawerk]

Oh, I am not very familiar with these Owon bugs, but one thing is clear. I am never gonna buy any Owon scope. Even their TDS series is crap when compared to GW Instek, Rigol, Siglent or Agilent. (Unless you really need a touch screen. )

[lemon]

Hydrawerk, "never say never".

This conversation about improvement of adapter circuit takes place only for older adapter versions.
For us to participate to this, is something like exercise to play with this circuit. The osciloscope is fine for measurements, there is no any problem about this.
Today this issue there is no exist and all the Owon SDS oscilloscopes are gnd noise free.

Owon starts (in some cases) to cover by warranty some customers via the dealer who sold the problematic oscilloscope. Perhaps, Owon starts to learn how to support the customer after sales.

We don't know how "crappy" is the TDS Series, there is no any review about this only photos and some technical characteristics.
But, the things is not paradise to other bigger companies. For example, the Rigol DP-832 is the recent case of problematic unit (I am owner of this) with problems that is more major from initial gnd-noise of Owon.

[Hydrawerk]

We don't know how "crappy" is the TDS Series, there is no any review about this only photos and some technical characteristics.

Well, according to the manual, the TDS has:
-no digital channels
-no intensity grading
-no signal generator
-no fine vertical controls
-no serial decoding
-no USB port on front panel
Well, we needn't call this TDS scope crappy, but it is no competitor for Rigol or GW Instek

[TomC]

Hydrawerk,
I'm just trying to understand your reasoning!
Do you own a scope? If so, how did you decide it was the right one for you?
From your post, I get the impression that you value a number of unrelated features. Do you actually have applications in your line of work for all of them?

For my needs, the only feature on your list that I wish my SDS scope had is the fine control.

However, if you do actually need all these features and are willing to pay for them, then you are right!
The SDS and TDS scopes shouldn't be on your list.

However, keep in mind that different users have different needs, and a list of features is just that, a list!
So when you say that the SDS and TDS are no competitors for Rigol or GW Instek, I hope you mean that this is true as far as your own personal needs are concerned, and are not presuming that this should apply to all other users.

[lemon]

I agree totaly with the TomC.

Additional this thread is for SDS Series and not for TDS. TDS Series have their own thread and is better any talk to be there.
TDS Series aren't available yet and we don't know which is their target group.
Personaly I haven't any information about this.
Personaly, I haven't any love with a specific trade.
For me and my economical situation the vfm is critical factor to buy a device.

SDS Series now they are good oscilloscopes for the price that they have.
They have some basic fw and some functions are missing like fine control tuning but at least these fw haven't bugs.

[BravoV]

Oh, I am not very familiar with these Owon bugs, but one thing is clear. I am never gonna buy any Owon scope. Even their TDS series is crap when compared to GW Instek, Rigol, Siglent or Agilent. (Unless you really need a touch screen. )

Why I feel you love to troll around ? Like jumping in a thread like this where owners are  discussing "specific" scope model and bashing it like there is no tomorrow ? And I noticed you did that at Rigol thread too. And its funny the brand GW Instek always pop out at this typical post of yours.

Its become tiring to read it too often, and you should know it better post like this is not going to be welcomed.

[lemon]

Well, the talk is LED Backlight Circuit about (Adapter Version 3.0).

The main dc-dc convertor marks 5126x and it is a G5126 High Efficiency, Constant Current, Boost DC/DC White-LEDs Drive of Global Mixed-mode Technology Inc. (Taiwan Company).
You can find the pdf here

At the attachment files there are one photo of this pcb area and the diagram from datasheet of this IC.

Owon seems to follow the directions of manufacturer, there are two decoupling capacitors C40, C41 at the input supply , there is an inductor of 10uH between input and LX and so on.
The only that missing is the 1uF output capacitor that there is a position for that but it is empty (C35).
Unfortunately, there isn't any significant improvement of this circuit and it has problematic supply at the input because it is sharing with other sources.
The input voltage of IC measured at 5.54Vrms when the datasheet refers range of power supply 2.7-5.5V. A little bit critical to my opinion.
The output voltage of this IC measured at position of C35 at 8.765Vrms with the Backlight to 0%.

At my next message, I'll present some small improvements to this area.

[rf-loop]

Owon seems to follow the directions of manufacturer, there are two decoupling capacitors C40, C41 at the input supply , there is an inductor of 10uH between input and LX and so on.
The only that missing is the 1uF output capacitor that there is a position for that but it is empty The output voltage of this IC measured at position of C35 at 8.765Vrms with the Backlight to 0%.

This datasheet circuit is ok only in principle. But not in practice if look how it need do in real life.
About voltage in position of "missing" C35 (I recommend install there some small good ceramic capacitor instead of electrolytic what have nothing to do there - exept if want some decorative reasons). (in real it is not missing but it is in totally wrong place after long trace - if it is there near TFT Led connector.) Voltage is what it is. Important is current and it is current controlled. In 100% position current is around 200mA as described in Cimei-Innolux (TFT) datasheet. What voltage it give over series connected leds (voltage may vary dependent of led manufacture lot and temperature etc) is not very important. I have measured some amount different voltages in different individual scopes. (mostly some amount higher if I remember right)

In 2011 this circuit was this (and note: backlight brightness control range was more wide)


This circuit need good bypass capacitor in its input and its output. (there is not)
In some versions output capacitor is also behind long PCB trace and this is totally wrong and also as in many cases, there have been even crap electrolytic only alone, and this is just like nothing with these risetimes and frequencies. Just becouse they follow only this kind of datasheed principled schematics. (and same problem in some other circuits)
In this kind of SMPS, both current loops need be low inductance and if want avoid common mode noise in GND these current loops over  GND need isolate from common GND area using "single point" connection so that this RF current do not fllood around ground. This PCB "topology" is terrible if think EMI.  They have tried break all possible rules what can break if want design low EMI circuit.

Brightness control is different (freq/duty)

Input and output need bypass very tightly and as close as possible.
Today current sense resistor (R17 in this image) is typically 1R0.

22 Feb 2013, 18:54    Post subject:     
--------------------------------------------------------------------------------
 
This old information is obsolete for 2012 and 2013 versions

2011 end, 2012 whole adapter board have been under development and it have changed many times! Sometimes less, sometimes radically.

Also in adapter board TFT backlight LED control have changed (many times) and freq are different. Also components are different. But still principle is same.

Last versions this circuit produce lot of noise and it need also modify on the aadapter board for less noise. (+ some other modifications for reducing GND noise.)

Backligt LED's current is important parameter and it need follow Innolux datasheet! 

Also note, control IC  have changed and it is not anymore 5126W.

[Hydrawerk]

Why I feel you love to troll around ? Like jumping in a thread like this where owners are  discussing "specific" scope model and bashing it like there is no tomorrow ? And I noticed you did that at Rigol thread too.

Well, DS2000 is a good bang per buck, there is no doubt.

And its funny the brand GW Instek always pop out at this typical post of yours.

Just because the GDS-2000A is quite nice scope with decent quality.

[lemon]

rf-loop very interesting information.
Yes, we are familiar with the changes that have done to Version 3.2 or 3.3, just this is like exercise to this circuit and how we can to improve with its limit.

I believe that I have followed your thought with these mods.
There are decoupling capacitors at the input and the output.

Here the tests before and after mods. The waveforms captures are with the tip of probe over the component without gnd connected anywhere.

All the spikes has gone. It is very interesting how eliminated all the spikes at the output.

Attachment files
mods.png = the mods on this area
L2.png = measurement over the L2 inductor
D12.png = measurement over the diode
IC.png= measurement over the EDS-5126
Output.png = measurement at the C35 position

[Hydrawerk]

Hydrawerk,
I'm just trying to understand your reasoning!
Do you own a scope? If so, how did you decide it was the right one for you?

Yes, a DSOX2002A. https://www.eevblog.com/forum/reviews/my-new-toy-%29-agilent-dsox2002a-sex-on-a-stick!/msg216361/#msg216361

If so, how did you decide it was the right one for you?

It is rather a long story... My friend had a bad experience with his Rigol. https://www.youtube.com/user/BigOne332137/search?query=rigol I wanted a scope with a free waveform generator. I knew many Agilent scopes from my university. They were easy to operate and very responsive. I was considering even the GDS-2000A, but I found out, that its Trig Out is weird.

[TomC]

Hydrawerk,
I'm just trying to understand your reasoning!
Do you own a scope? If so, how did you decide it was the right one for you?

Yes, a DSOX2002A. https://www.eevblog.com/forum/reviews/my-new-toy-%29-agilent-dsox2002a-sex-on-a-stick!/msg216361/#msg216361

If so, how did you decide it was the right one for you?

It is rather a long story... My friend had a bad experience with his Rigol. https://www.youtube.com/user/BigOne332137/search?query=rigol I wanted a scope with a free waveform generator. I knew many Agilent scopes from my university. They were easy to operate and very responsive. I was considering even the GDS-2000A, but I found out, that its Trig Out is weird.

Nice scope! Nice features!

However, the price tag of around US $1200 for a 70MHz scope would have eliminated it as a choice for my needs/budget. You see, I already own two 60MHz CROs, so for my first DSO, I valued a functional 200MHz bandwidth over a built in function generator. And with a price tag of US $430 for the Owon SDS, there would have been no contest between these two choices.

Good luck with your new scope, I hope you enjoy it!

[TomC]

rf-loop very interesting information.
Yes, we are familiar with the changes that have done to Version 3.2 or 3.3, just this is like exercise to this circuit and how we can to improve with its limit.

I believe that I have followed your thought with these mods.
There are decoupling capacitors at the input and the output.

Here the tests before and after mods. The waveforms captures are with the tip of probe over the component without gnd connected anywhere.

All the spikes has gone. It is very interesting how eliminated all the spikes at the output.

Attachment files
mods.png = the mods on this area
L2.png = measurement over the L2 inductor
D12.png = measurement over the diode
IC.png= measurement over the EDS-5126
Output.png = measurement at the C35 position

Those are amazing results!
The improvement on the output waveform is incredible, great job!

[TomC]

In some versions output capacitor is also behind long PCB trace and this is totally wrong and also as in many cases, there have been even crap electrolytic only alone, and this is just like nothing with these risetimes and frequencies. Just becouse they follow only this kind of datasheed principled schematics. (and same problem in some other circuits)
In this kind of SMPS, both current loops need be low inductance and if want avoid common mode noise in GND these current loops over  GND need isolate from common GND area using "single point" connection so that this RF current do not fllood around ground. This PCB "topology" is terrible if think EMI.  They have tried break all possible rules what can break if want design low EMI circuit.

I feel the same way,
A capacitor at the end of a long trace may help the output waveform, but where high frequencies or fast changing signals are involved, I don't think it will do anything to stop the energy radiated or capacitively coupled to adjacent circuits/traces by the long trace. You may not see a problem at the output, but the common mode noise coupled to other circuits/traces via the long trace will still be there.

[rf-loop]

Here the tests before and after mods. The waveforms captures are with the tip of probe over the component without gnd connected anywhere.

Good result with this  mod on this board version.

[Carrington]

More improvements. Now most of the noise comes from the local FM station 106.5MHz (previously I could not see this, because the SDS noise covered it). I have to paint the wall with conductive paint too... 

Owon, takes note!

[Carrington]

This circuit need good bypass capacitor in its input and its output. (there is not)
In some versions output capacitor is also behind long PCB trace and this is totally wrong and also as in many cases, there have been even crap electrolytic only alone, and this is just like nothing with these risetimes and frequencies. Just becouse they follow only this kind of datasheed principled schematics. (and same problem in some other circuits)
In this kind of SMPS, both current loops need be low inductance and if want avoid common mode noise in GND these current loops over  GND need isolate from common GND area using "single point" connection so that this RF current do not fllood around ground. This PCB "topology" is terrible if think EMI.  They have tried break all possible rules what can break if want design low EMI circuit.

https://www.eevblog.com/forum/testgear/review-of-owon-sds7102/msg263208/#msg263208

[lemon]

Thanks guys for encourage to my trials.

Carrington, your news is marvelous.
I am looking here to find Kontakt 35 or similar product.
When you have time, don't forget to upload the measurements after the apply of shielding.

[AndrejaKo]

Hi guys! I have a bot of time now so I want to try few more experiments.

@Carrington How much spray did you use to cover the inside of the scope? I'm thinking of getting Kontakt Chemie EMI 35 and apply it to the insides. My situation is currently reverse of your own. My scope jams all FM stations from 96 MHz to 97 MHz when on. Also any chance of screenshots of noise after the spraying?


@lemon I'll try your adapter board mods and report back the results.

If I remember correctly, there was one theory that mentioned noise on the sense pin of MC34063 is the reason for duty cycle change. If I understand how this works correctly, decreasing resistors on the pin should increase noise immunity, right? My PSU has a 9.07 kiloohm resistor marked R37 from the pin to the ground and 1.794 kiloohm resistor marked R40 from -7.6 V to sense pin. This should give nominal voltage of -7.569 V and current through the resistors of around 700 microamperes, if I'm right. I'll try with combination of 1.1k and 5.6k and see how that goes.

[TomC]

More improvements. Now most of the noise comes from the local FM station 106.5MHz (previously I could not see this, because the SDS noise covered it). I have to paint the wall with conductive paint too... 

Owon, takes note!

Nice paint job!

Did you fix your adapter board? Or did you get new boards from Aidatek?

[TomC]

If I remember correctly, there was one theory that mentioned noise on the sense pin of MC34063 is the reason for duty cycle change. If I understand how this works correctly, decreasing resistors on the pin should increase noise immunity, right? My PSU has a 9.07 kiloohm resistor from the pin to the ground and 1.794 kiloohm resistor from -7.6 V to sense pin. This should give nominal voltage of -7.569 V and current through the resistors of around 700 microamperes, if I'm right. I'll try with combination of 1.1k and 5.6k and see how that goes.

Yes, that's a possibility. Just looking at the values you propose it seems that you are keeping the same ratio, which is what is needed. Let us know what happened once you try it!

[lemon]

TomC, if you see at the Carrington's attachment photo the two boards are new versions (and the show is that the new PSU board haven't any mark again!)

AndrejaKo, I'll waiting for your results and observations, start at the first with the LED Backlight mods.

[TomC]

TomC, if you see at the Carrington's attachment photo the two boards are new versions (and the show is that the new PSU board haven't any mark again!)

AndrejaKo, I'll waiting for your results and observations, start at the first with the LED Backlight mods.

Good eyes!
I missed that on my first  view.

[Carrington]

Thanks guys for encourage to my trials.

Carrington, your news is marvelous.
I am looking here to find Kontakt 35 or similar product.
When you have time, don't forget to upload the measurements after the apply of shielding.

With shielding.

Edit:

  - On DSC04301.JPG probe X10, i.e. real Vpp noise is 2.8mV. Because this noise come from the big gnd loop.
  - Note the peak over 106.5MHz, i.e. internal FM receiver Osc. to get 10.75MHz IF.