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

[Siri]

...
These "low ESR" electrolytic capacitors are good as long as there need handle low frequencies but they can not do nearly anything in this frequency area.  4mm long, 0.25mm copper wire is around 2.5nH. ( 100MHz XL is around 1.6ohm) Now I ask what is low ESR capacitor real impedance with 100 to 200MHz.)   How about PCB GND trace impedances with this freq?

(btw: I know Owon is now working for this)

Of course the problem of "noise" inherent principle of pulsed sources, literacy circuitry and component selection. There are special (with an operating frequency of up to several hundred kHz) series of capacitors with Low ESR and impedance. Though there main goal is to reduce the output voltage ripple.

In the first review, I did not see obvious blunders in the topology of the adapter board. But I'm not a super expert in this. Perhaps the noise comes from the absence of the rule of "one point of common ground." Also, it is likely that the sharp edges on "the ring" of their spurious own resonance in inductors. For example, I see that in my converter +5.5 installed in 5.6 uH inductance, and the photo of the former unit of 2011 MY this inductance is 15 uH.
And I think in the devices in 2011 in this converter used a different chip.

my bad English ... Sorry if there are awkward phrases

(UPDATED)
Hooray. A simple solution is almost completely eliminated the "GND-noise" of the converter +5,5V in my version of the adapter board. Overall noise level dropped by nearly four times.
Most were noise from the circuit display.
Details tomorrow (ie today, Moscow time).

[StubbornGreek]

or maybe DIY instructions of how to repair it?

I would be happiest with this option.

Thanks rf-loop and siri for contributing on this issue.

[DrBob]

(UPDATED)
Hooray. A simple solution is almost completely eliminated the "GND-noise" of the converter +5,5V in my version of the adapter board. Overall noise level dropped by nearly four times.
Most were noise from the circuit display.
Details tomorrow (ie today, Moscow time).

Hey Siri:

The suspense is killing me!

[Siri]

As suggested earlier, the important cause of failure in the topology switching powers.
The simplest solution to slightly reduce the gnd-noise converter +5.5V is a way of shortening the path length of the pulse current on copper coated PCB. To do this:

- Turn the D127 so that its anode connected to the ground at a nearby ground, next to the hole mounting board to the metal Z-base (pre-need to clean and tin the landfill site for a new soldering points):



- Cut the two ground wires from the connector of adapter board and solder them to the ground plane in soldering the anode of the diode. The photo below is the place indicated "Better." (It is seen as the beginning I tried to connect the wires to the GND in the corner of the polygon adapter).



In my case, the noise from the converter +5.5V decreased by three to four times. But now was significant noise from the pulse backlight TFT circuits +8,6...9,5V.
By the way, I tried to disable backlight switching circuit and power the lights directly from the circuit +8.4 V. Brightness greatly reduced and therefore the oscilloscope was almost impossible to use, but the noise was almost no more.

[AndrejaKo]

Interesting bit of research!

Also I'd like to thank you for awesome illustrations!

[DrBob]

As suggested earlier, the important cause of failure in the topology switching powers.
The simplest solution to slightly reduce the gnd-noise converter +5.5V is a way of shortening the path length of the pulse current on copper coated PCB. To do this:
...
In my case, the noise from the converter +5.5V decreased by three to four times. But now was significant noise from the pulse backlight TFT circuits +8,6...9,5V.
By the way, I tried to disable backlight switching circuit and power the lights directly from the circuit +8.4 V. Brightness greatly reduced and therefore the oscilloscope was almost impossible to use, but the noise was almost no more.

Hi Siri,

Great investigation and supurb illustrations. It was worth the wait.

Can you show us an example of a trace from your files showing the ground noise before the mod and a similar trace now?

Thanks for all your hard work.

[Siri]

Hello DrBob!

As I said it reduces the overall noise somewhere in the 3-4 times. Tomorrow I'll post my final image noise. BUT! It will not be very relevant to this modification pictures, will be slightly better. After this upgrade, I had a deeper (and really "hard work" ) with a desire to further improve results. This includes trying to improve the topology of backlight pulse circuit. In the end, it's my adapter board has quite jaded view

[alexuresp]

https://picasaweb.google.com/107445062668018969562/DropBox?authuser=0&authkey=Gv1sRgCMeok-GdvqTjGA&feat=directlink
Thats my noise after soldering. It seems that the ripple  smooth or simply tightened. Can be compared with the photo Siri on previous pages. GND  is not cut from a  line.
Still bad, frequency in main spike  nearly 87 MHz

[rf-loop]

Thank you Siri about this Diode turn. Good finding!

(whole "noisy GND" case is under work in Owon)

After 2011 there have been many modifications on the Adapter board. If look old 2011 board and today board it is difficult to think they are from same SDS model. And between these there have been many many changes after changes.

Also note that after this version what "Siri" have there is many changes in Adapter board.

V3.2 board TFT backlight LED power circuit is also changed lot of between these versions.

This version is like jammer transmitter. (but it is easy piece of cake in this whole "noisy GND" case.)

But solution for one version is propably not solution for other version!

This main problem is that whole GND mess is like "magpie nest" if think high frequencies when switching circuits works.

Switching current loops in separate SMPS circuits are just like kids design who have only designed DC things. Perhaps after it have started to modify after 2011 somebody have forget to watch noise when he change layout.
 
Good  (just one simplest) example is this C34. What hell this designer have thinked when he handle this switcher output. Perhaps just nothing but next lunch time.
(picture is from factory original SDS7102   adapter board V3.2.)

[Siri]

Thank you Siri about this Diode turn. Good finding!

This idea was suggested to me in correspondence my Ukraine colleague alexuresp. Thanks to him!

Can you show us an example of a trace from your files showing the ground noise before the mod and a similar trace now?

Below the picture noise my SDS7102v after deep changing adapter board. Measurements made in the same place, and the conditions and rules in my post earlier. Let me remind the noisiest sites in my previous study revealed dc-dc converter +5.5V and pulse circuit TFT backlight. I will repeat here the old pictures for comparison.

But it all worked out to get not just "turn" of the diode. Were made much larger changes in the adapter and I can not recommend it because of the complexity and individuality of this work.



First the overall picture noise.

So it was:



Thus it became:




So it was:



Thus it became:




The noise of the dc-dc converter +5.5 V.

So it was:



Thus it became:




The noise of pulse circuit TFT backlight.

So it was:



Thus it became:




So it was:



Thus it became:




And finally, an example of a picture waveform from the built-in generator (with a tip-hook and  with the ground wire-crocodile, probe in position "X10").

[alexuresp]

Hi guys  i got a perfect solution i think.
https://plus.google.com/photos/107445062668018969562/albums/5847922453850803761/5848219105755079794?authkey=CMeok-GdvqTjGA&banner=pwa&gpsrc=pwrd1#photos/107445062668018969562/albums/5847922453850803761/5848219105755079794?authkey=CMeok-GdvqTjGA&banner=pwa&gpsrc=pwrd1
Thats easy and u can try, but need small one to close the case.

[Siri]

Aleksandr, ne znal otkuda ti sam i seychas popravil svoy post na "ukraiskogo kollegu"

Kstati ferritovuyu zashelku na schleif provodov ya poprobobal stavit' srazu, no u menya eto ne dalo bol'shoy polzi. U tebya namnogo snizilsya shum?

[alexuresp]

Da shum upal prilichno, no eto v komplekse so vsemi peredelkami.
Dumayu esli postavit' ferrit to mojno zemlu ne brosat' na pryamuyu. No korpus ne zakrivaetsia iz za ruchki, mojet prosto poprobovat' obmota' ekranom shleyf. No nujen skotch takoy.
Otot gorb na fotah v albome pochti ne vidno.

dobavil fotki v al'bom mojno sravnit'


The noise is not gone, it became less and filtered. This is not ideal, and for each will require a different approach.
Perhaps Owono correct it in the next version and break something else%)

[Siri]

Da shum upal prilichno, no eto v komplekse so vsemi peredelkami.
Dumayu esli postavit' ferrit to mojno zemlu ne brosat' na pryamuyu. No korpus ne zakrivaetsia iz za ruchki, mojet prosto poprobovat' obmota' ekranom shleyf. No nujen skotch takoy.
Otot gorb na fotah v albome pochti ne vidno.

U menya v itoge minus podayetsya vse-taki na ugol platy, kak na fotke raneye. No sama plata perepakhana tak chto strashno smotret'.
Nu i nizhe rasshifrovka dlya nenashikh tovarishchey.

(Ferrite clip tried before, but the result is small.
I finally did gnd wires served by the angle of the board as in the photo above. But the board plowed so scary looking.)

[rf-loop]

Some kind of an interim report.

Here compared factory original with "noisy GND" issue and same model but modified.
Compare made parallel so that all other things eliminated. Same time, same enviroment EMI noise level.
 
Both are same version SDS7102 and both powered using same AC source.

Test setting you see in images. Probe is set for 10:1 so that its freq response is full. All tests used same probe and compensation adjusted only with modified oscilloscope. (you can see small difference becouse scope inputs capasitances are not very exactly same)


These test setup is made so easy that everyone can do this same test without any external equipments.

Note memory selection!




Probe hook and probe own long GND wire (both) connected to Probe Compensation output GND.
(If use probe tip directly + very short GND wire connected to GND it do not show this noise becouse there is not GND wire "high" inductance.)
 


Unmodified



Modified



Probe 10:1 and tip connected to Probe Comp out and probe own long GND wire connected to probe comp out GND.
Note Offset setting! Whole signal level (5V) from peak to peak is 100 div vertically!


Unmodified



Modified.



Work is not ready.  Experiments, tests and work for finding best way for (simple) DIY solution is still under work.
Also waiting Owon official version for solve this problem.

[Siri]

Nice work, rf-loop.

Vertical level 50 mV here with the probe X10 (ie, the actual level of 5 mV/div input)? If so you get a very good result!

Below is the gnd-noise my modified 7102 under the same settings (probe X10 with hook and long gnd-wire. 50 mV/div - the real input level of 5 mV/div):



The remaining noise is derived from the periodic pulse train in the circuit TFT backlight:



I wonder how you managed so well to reduce noise backlight?

[alexuresp]

But the remaining noise is huge, we should try to filter it better.
On my GND noise the biggest level 60kHz from power supply.
fixed

Now the main noise from LCD.
rf-loop how you fight with this ?

[Siri]

Alex, u tebya vertikal'nyi predel 50 mV pri X1. Sdelay na 5 mV.

(U menya na fotke vishe 50 mV/div eto pri ustanovke X10, t.e. fakticheski tam 5 mV po vhodu esli X1)

[unl34shed]

Hey guys,

I have a small problem with my SDS7102 and hope you can help me.
The problem is, that the Scope starts to hang-up after a while. The LED starts to get RED, the Owon support said that this means the battery is charging but i don't have one 

I think it is a temperature or PSU problem (or both) because the supply Voltage seams to break down (Fan gets slower)
Just want to know if anyone of you knows anything about that and how to solve it or if the problem is new.

HW-Version is 710243XX
LAN-Port only, no VGA, no RS232

Hope someone can help me

[rf-loop]

Hey guys,

I have a small problem with my SDS7102 and hope you can help me.
The problem is, that the Scope starts to hang-up after a while. The LED starts to get RED, the Owon support said that this means the battery is charging but i don't have one 

I think it is a temperature or PSU problem (or both) because the supply Voltage seams to break down (Fan gets slower)
Just want to know if anyone of you knows anything about that and how to solve it or if the problem is new.

HW-Version is 710243XX
LAN-Port only, no VGA, no RS232

Hope someone can help me

Perhaps your HW is 7102 1143xxx ?

Do you have any start up problem or any problem during use. Only problem is led color or any other problem?
You tell that FAN speed also drop.

(oscilloscope nominal internal main voltage without battery is 8.4V  but its accepted range is around 6.6 to 8.4V  and FAN runn with this voltage. All other needed voltages inside oscolloscope are derived from this around 6.6V to 8.4V main power and they stay still constant.)

You have no battery. Normal is that it works with around 8.4V (and if you turn battery indicator on it show normally in this case full battery - you can look it)

If this voltage drops randomly it tell that somewhere is problem. Problem may be on the (1. suspect) PSU itself or there is (2. suspect) extra load due to some internal fail in other parts than PSU itself.  Situation is not normal if without battery these leds suddenly/randomly go red and also you can hear FAN speed drops. Still your scope may work normally. (if problem is PSU, as long as it keeps voltage over lowest acceptable)
 
Later if this problem go more bad it perhaps stops working. If Owon do not repair it now, then they need repair it later after it stop workig. As long as it works normally it do not have status "failed".
Also if it do it only sometimes just randomly...   it is difficult case in service. Perhaps it do not go to this state in watching period.

You can turn it on and keep it on continuously example one week  or run it behind timer... 3 hour on, 1 hour off... let it go until fail.

[AndrejaKo]

@RF-LOOP
Now that you mentioned battery indicator, I have a question:

Would battery indicator showing slightly discharged battery when the battery itself is removed from the scope be a sign of PSU problems? How does the indicator work on this scope? Just measure the voltage? Or is it doing something smarter?

[rf-loop]

@RF-LOOP
Now that you mentioned battery indicator, I have a question:

Would battery indicator showing slightly discharged battery when the battery itself is removed from the scope be a sign of PSU problems? How does the indicator work on this scope? Just measure the voltage? Or is it doing something smarter?

If it show slightly discharged without battery, it looks like there is not full 8.4V power supply output.

Indicator is just as simple as it can be. It do not know anything but just voltage.

Reason for low voltage is PSU or internal extra load. My quess is PSU.

If you measure be careful: do not make short circuit! There is no fuse.
 (batt over current protection is inside batt module)

[AndrejaKo]

Thanks a lot!

[Timmy]

Has anyone used the trigger holdoff on the SDS7102? I tried to use it today, but it seems that it only increments by 100ns at a time. I turned the knob for a minute and only got to 1ms. How in the world am I supposed to get to something like 100ms without turning the knob for an hour and a half? It's supposed to go up to 10 seconds.

[TomC]

Has anyone used the trigger holdoff on the SDS7102? I tried to use it today, but it seems that it only increments by 100ns at a time. I turned the knob for a minute and only got to 1ms. How in the world am I supposed to get to something like 100ms without turning the knob for an hour and a half? It's supposed to go up to 10 seconds.

On mine, the faster you turn the knob the larger the increments. Still, it takes a while to get to 10S.