nothing against what you say - it depends on the way the ground distribution is done.
Another thing that must have been designed/decided by a dev engineer who rather should be kept away in an assylum for mental cases.
And of course I noticed already the noise radiated from the display but there is no way to say anything defenitely about that as long as these many connecting lines between Main PCB and display all running along on the I/F PCB in close vacinity under 4 of these little switchers. This I/F PCB acts as a perfect coupling device to make sure that all spikes are properly distributed over the entire machine.
You see the display itself works at a relatively low voltage level signalwise, haven't checked that yet - perhaps around 3V whereas the switchers work from 8.4V and some amps are flowing.
So what would you guess makes more noise, a bunch of low current / low voltage signals or high current square waves at up to 8.4V.
And should the radiation going out from the front of the dislay be too much for you you get yourelf one of this conducting but transparent microfabrics that Tek offered as an option for all of its scopes for environments that are highly sensitive to noise radiation. You know, a normal CRT radiates as well out of the screen a little...
I think we can handle all of this.
And after we have designed a small pcb for all the little switcher beasts and put them inside of a small tin box that will be screwed through isolated posts above the I/F PCB with no noise going outside of this box and the outputs connected with if you want shielded cables to where the voltages should really go I'm sure we have that thing cured.
And, I tell you if this spreads around the price for this machines will fall and whoever feels like may offer a kit with all inside what we did (will not be me for sure will be off to new shores then) to convert this bastard to a decent device.
Just search ebay for this owons as I did recently. Countless offers came up. Piles of this machines must be out waiting for uninformed buyers. Do you know what I means....?
The marks on the chips in my machine are:
upper one: OBT 24J PDVH
lower one: 1780 TB51
Hi Tomc,
I' sorry but I think that you want to qualify a 'deplorable state of affairs' (got it from the Dictionary) and what the heck should that help as we already know what's it's cause.
It's like counting the red spots after somebody got the measels instead of giving the right medicine.
You qualify and count red spots if you want to optimize a thing not when you have a basic, well known and documented problem.
At 100MHz a short piece of wire acts already like a coil. So what does it help using probes to qualify the prob here. It might help to find out that there is a prob but thats it.
What you explaind is absolutely right - common mode / differential mode - but is again just a refined description of the problem.
You know a machine radiating HF is like a transmitter. you have antennas, traps, ample return pathes, stray capacitances/inductivities and whatever. It will act differently if you move it from a desk made out of dry plastic to a desk made out of wood that stood before outside in the rain.
Radiation return path takes place through the mains cord but also through the electrical/magnetical fields. All of this has absolutely chaotic nature here!
If you do not want a machine to act as a transmitter kill or shield the source of the signal that makes this machine act like a transmitter not qualify how good or bad it acts as a transmitter.
Concentrate on what has to be done to make the thing work fine.
Personally, I'm satisfied with these results. Of course they are not perfect, there is still a little ground noise, but it no longer hinders my ability to use the scope to view low level signals when I choose to use the 6" ground lead.
By the way, the LCD panel is large source of radiated noise, but it's only a problem if you get the probe cables close to it.
In addition, how you get rid of all the noise sources that don't come from the oscilloscope?
So once more: YOU DO NOT DECIDE THE LENGTH OF THE GROUND LEAD YOU USE ON YOUR PROBE ACCORDING TO THE NEEDS OF YOUR SCOPE BUT IN ACCORDANCE TO WHAT MEASUREMENT YOU HAVE TO TAKE!
If you can live with it no problem for me, but in everydays work you will have to face the limitations sooner or later. And in a serious technical discussion it's just not very helpfull.
Hi tomC,
just reading your post with the pics.
Please can you make a pic series using setup of pic #3 (a bit more amplitude would help) and sweeping the generator from say 50KHz up to say 150Mhz or max to see how much the cores on your probe and the ground lead 'tank circuit' affect the frequency response. A fast rise squarewave test at perhaps 100KHz to 10MHz would also do I think, but don't know if you have such a generator. And please care for correct termination on the output of your generator(s). (If the generators output is 50 Ohm put also a 50 Ohm termination before connecting the probe.
And please do the test twice with the probe in x1 and x 10 mode.
And it would be of good practise if you do the tests first of all as a reference with the generator(s) connected through a BNC cable directly to the scope with enough amplitude so that 'noise << signal'. Here the termination has to be on the scope side of the cable (Generator -> BNC cable -> termination -> scope).
Thanks
And, I asked you alredy once but you obviously forgot: Can you please explain in short the mechanism of the belly strap you added. I think it's used often on transformers if I'm right - a chopper band around the outside - but cant' remember having seen that on power transistors or FETs. Have to admitt have not yet read the additional literature concerning denoising perhaps it's in one of these.
....
Haven't installed it yet, but apparently for anything higher than 1211xxx you get version 3.8.
Don't remember what version is your unit but I think you said it was purchased 2012.
Sorry, now I see it!
What you are thinking about installing?
Nice to see you TomC again
By the way, my wishes for your birthday (soon)...to be very well with your family.
I am looking about fw, with yours serial and the result was the same Ver. 3.3!
You have downloading and installed the fw to your scope or downloading only and saw some txt file?
You have fine memory, mine was 2012 series (1211xxx).
And one more fact. On a 350MHz scope I think it's probably not so advisable to 'slow down' the probe with a ferrite core. You know the ringing caused by the spikes is generally above 100MHz so it doesn't bother you so much probably.
Thanks a lot so far and please cross you fingers for me not to send any of those chips to heaven.
Hi to everyone, specially to TomC & Carrington.
I see that the member Sarasir had doing a lot of interesting work about eliminate the noise floor of this scope.
Personally, I have stopped the development about noise issue, after the last psu and adapter board changed.
For a long time ago, I will wait a fw development from Owon....
Now, I see that they give us the version 3.4 but for only newer s/n scopes !
Copy from their site:
SDS7102UP3.4
29 May 2014
The firmware applied to the products with following production batch / serial no. -
SDS71021312xxx, SDS71021319xxx, SDS71021327xxx, SDS71021344xxx, SDS71021352xxx, SDS71021407xxx, SDS71021414xxx, SDS71021418xxx,
Change log - :
1. XY mode - persistence function added ;
2. waveform refresh rate improved ;
3.waveform cutting/ recalling function added;
4. autoset - waveform recognition;
5. channel invert bug fixed;
6. probe attenuation compensation;
7. recorded waveform exported to USB drive
8. automatic measurement - 4 more options available
9. vertical position over-speed movement bug fixed
Have someone, any kind of information what is happening with the older s/n?
Nice to see you TomC again
By the way, my wishes for your birthday (soon)...to be very well with your family.
I am looking about fw, with yours serial and the result was the same Ver. 3.3!
You have downloading and installed the fw to your scope or downloading only and saw some txt file?
You have fine memory, mine was 2012 series (1211xxx).Sorry Lemon, I didn't catch what you were trying to tell me with the pic when I first read your post, yes, that's the firmware I downloaded, and even though it says V3.3, it's the same file that is used for the later models listed as V3.4. That V3.3 is what I installed on my scope, but it gave me version 3.8, with apparently all the new features that the change log lists for theoldernewer models. Don't know why Owon makes the listing so confusing, it appears that the same file is used for the whole SDS line.