VOLTCRAFT DOV series

[evava]

What is actual purchase price of the scope ( 2 and 4 channel) with VAT at this time?

https://www.idealo.de/preisvergleich/OffersOfProduct/210577094_-dov702-digital-oszilloskop-70mhz-2-kanal-1-25gsa-s-12bit-vc-16753905-voltcraft.html

https://www.idealo.de/preisvergleich/OffersOfProduct/210287612_-dov704-digital-oszilloskop-70mhz-4-kanal-voltcraft.html

Could anyone guess why the cheap prices are only for Germany and Austria?
I think the former Eastern Bloc countries are much more price sensitive, and there sales at German prices (Voelkner) would probably break records.

[Martin72]

I had already complained that there’s no axis labeling that you can turn on or off.
I just saw in the 800 series manual that there’s supposed to be a feature like that... That would be so ridiculous if it were true...
@Microcheap, do you have this feature in the display menu?

[Aldo22]

Could anyone guess why the cheap prices are only for Germany and Austria?

Conrad Austria charges regular prices.


The promotions are only available in Germany and Switzerland afaics.
I have no idea why only there.

[Aldo22]

I had already complained that there’s no axis labeling that you can turn on or off.
I just saw in the 800 series manual that there’s supposed to be a feature like that... That would be so ridiculous if it were true...

Hasn't that changed with the firmware update?

[Aldo22]

Then something is definitely wrong.

I have a slightly more general, somewhat theoretical question about this:

Is it even possible that my device has a hardware fault or discrepancy that only affects the FFT?

The signal is clean; the amplitude and frequency measurements are correct.
I don’t know much about this, but it would make sense to me if this signal were processed further only via software.

So could a hardware difference (compared to Martin’s device) be responsible for the difference in the FFT display, or is that actually out of the question?

For those who haven’t been following: Same PCB with 2 or 4 channels, same firmware, just a different version.

(I could simply try upgrading the hardware, but unfortunately I can’t downgrade)

[Martin72]

Hasn't that changed with the firmware update?

No, otherwise I would have mentioned it.

Is it even possible that my device has a hardware fault or discrepancy that only affects the FFT?

Right now, I find that hard to imagine.
There are a few Voltcraft/Owon owners here; if one more person posted their FFT results, that wouldn't be bad.
YOU could update the firmware....
Yeah, I know, the fan.
But if the update didn't help, I'd return the scope anyway if I were you.
If it did help, you can always make the fan quieter.

[Aldo22]

Right now, I find that hard to imagine.
There are a few Voltcraft/Owon owners here; if one more person posted their FFT results, that wouldn't be bad.
YOU could update the firmware....
Yeah, I know, the fan.
But if the update didn't help, I'd return the scope anyway if I were you.
If it did help, you can always make the fan quieter.

One day, my curiosity will probably get the better of me.
But right now, I only know of one drawback to the new FW version (Fan) and no confirmed benefits. That’s why I’m in no rush.
If I could go back, I would have tried it already.

For now, I just want to rule out the possibility that an individual hardware defect is responsible for the difference in FFT.

I find that hard to imagine, and apparently so do you.
By the way, it’s exactly the same on both channels.

Thanks. 

[Olex]

A bit off-topic from the bugs.

There are many hidden menu items in the Android settings.
I discovered the ability to install your own apps.
To do this, go to settings, search for "security" in the search bar, and open that section.
Then, enable "Unknown sources" (this needs to be reactivated after restarting the device).
After that, installing your own apps works.

In addition to this, when powered on while holding the Home button, the oscilloscope enters USB Download mode.
At this point, fastboot starts working, which opens up opportunities for further exploration and hacks.

Code: [Select]

$ fastboot devices -l
????????????           Android Fastboot
 usb:3-1

$ fastboot getvar product
product: s5p4418
Finished. Total time: 0.000s

$ fastboot reboot
Rebooting                                          OKAY [  0.000s]
Finished. Total time: 0.101s


[Martin72]

That’s why I’m in no rush.

Then I won't be either.

[Aldo22]

There are many hidden menu items in the Android settings.
I discovered the ability to install your own apps.
To do this, go to settings, search for "security" in the search bar, and open that section.
Then, enable "Unknown sources" (this needs to be reactivated after restarting the device).
After that, installing your own apps works.

Brilliant! It works! 

[Aldo22]

That’s why I’m in no rush.

Then I won't be either.

Well, it seems there are still a lot of new findings, so we can see if any new opportunities arise.
I just came across this because of Olex's post.
I wonder if this means a complete reset to the original FW version (probably not, only data)

[Martin72]

If you're unlucky, the “Oscilloscope” app might get deleted too; I'd leave it as is.

[Martin72]

I've now contacted Owon.cn regarding the “ripples,” but I simply haven't received any further response from Owon EU.
The only response I got was a request for the purchase location, invoice, and serial number.
As I've said before, the Chinese rarely—if ever—have technical support; it's always just the salespeople trying to make a sale, and either they brush you off with empty platitudes, or they say they'll check with the tech department, or they don't respond at all.

[Aldo22]

I've now contacted Owon.cn regarding the “ripples,” but I simply haven't received any further response from Owon EU.
The only response I got was a request for the purchase location, invoice, and serial number.
As I've said before, the Chinese rarely—if ever—have technical support; it's always just the salespeople trying to make a sale, and either they brush you off with empty platitudes, or they say they'll check with the tech department, or they don't respond at all.

Oh, right, I also received a response from Conrad.

“We have received feedback from our quality assurance department. They inspected the device and determined that there is no defect, provided it is set up correctly. We therefore assume that an external factor on your end may be responsible for the meter’s behavior.”

Did I hope for a better answer? Yes!
Did I expect a better answer? No...

[Martin72]

They inspected the device and determined that there is no defect, provided it is set up correctly.

"If you don't use the 200 mV/div or 10 V/div settings, you won't have any problems.".....

[KungFuJosh]

For now, I just want to rule out the possibility that an individual hardware defect is responsible for the difference in FFT.

Have you tested the same sig gen output settings for FFT on another scope yet?

[evava]

So, I’ve put together a small table—using Channel 1 as an example, but it applies to all channels.
Specifically, it shows the switching states of the two relays per channel in the front end.
What stands out in this overview is that there are only two situations where the ripple appears: at 200 mV and 10 V—and in both cases, RL30 is switched on.
That’s a lead I’ll be pursuing further.

Martin

If I had this oscilloscope at hand, I would try connecting a capacitor of about 100 to 200 microfarads to the relay RL30 (its coil) to see if the ripple on the 200mV range changes (reduces).

[Aldo22]

Have you tested the same sig gen output settings for FFT on another scope yet?

Yes. Look, my Hantek is really a very simple and inexpensive oscilloscope, but it clearly shows me the difference between a square wave and a sine wave, along with a dB reading that at least seems plausible, without me having to spend hours trying to adjust something without success.
With the DOV, everything usually jumps around, and the dB readings don't make any sense to me, no matter what I try.

[KungFuJosh]

Does it help at all if you increase the output level of the sig gen?

[Aldo22]

Does it help at all if you increase the output level of the sig gen?

No, why should it?
That depends on the V/div setting, doesn't it?
In the screenshots above, there are 2 Vpp; that should be enough.

[KungFuJosh]

Should be enough. But signal quality and dynamic range can be related to output level, especially with less expensive tools. Maybe there's too much noise for the DOV to handle it? I dunno. It's worth a shot.

[Olex]

I just took an FFT screenshot using a rather mediocre generator I had on hand.

[KungFuJosh]

I just took an FFT screenshot using a rather mediocre generator I had on hand.

Mediocrity is relative.

Please try with consistent settings for comparison:

To be able to compare anything, the conditions have to be reasonably similar.

12.50 MHz at 4 Vpp with coax and a 50-ohm load = approx. 2 Vpp.

[Lutz21]

I also do not have a nice generator, 2 Mhz with a little longer timebase.

[Martin72]

If I had this oscilloscope at hand, I would try connecting a capacitor of about 100 to 200 microfarads to the relay RL30 (its coil) to see if the ripple on the 200mV range changes (reduces).

I don't know if that will help, because the ADS900A has the same board/front end and is configured exactly the same way in that area.
I just know that the interference is there (or occurs) when RL 30 switches.
All front-end relays are connected to the same supply voltage via a resistor.
This, in turn, also supplies the positive rail of the op-amp power supply in the front end.
What I can do is manually switch a channel as an example—that is, deactivate the relay—so we'll know for sure if that's the cause.