VOLTCRAFT DOV series

[Olex]

Here is a slightly more detailed schematic that I was able to create by measuring the circuit.
The component with the code “ST3SK” has me a bit stumped.
Is it another op-amp, or is it something else....
In any case, the ripple can be measured at the output of the first op-amp, then at the output of the second, where it goes to the relay contact.

Martin, did you happen to look at this noise on the op-amp power supply lines and on the pins of this mysterious ST3SK?

[Martin72]

Hi,

https://www.eevblog.com/forum/testgear/voltcraft-dov-series/msg6287666/#msg6287666

https://www.eevblog.com/forum/testgear/voltcraft-dov-series/msg6288624/#msg6288624

Of course, I also took some measurements in this context.
The +5V line, which powers all the relevant semiconductors there, shows slight spikes in the 40 kHz range.
I can’t say at this point to what extent these are also amplified.
The 5V rail sometimes has to cover quite a distance; for example, the voltage drop between the 5V supply in the first channel and the fourth channel is almost 70 mV...
Perhaps this 5V supply is buffered more frequently “along the way” in the MSO version—that would be one theory.

[Aldo22]

So, here is the fix for the fan speed control, which was broken in the new firmware version (V1.0.1.0.17).

I really appreciate your efforts to improve the DOV.
Great job. 

When it comes to the fan speed control, though, I'm not entirely sure if Owon really messed that up, or if it was intentional—for example, to improve stability.
What do you guys think?

[Olex]

So, here is the fix for the fan speed control, which was broken in the new firmware version (V1.0.1.0.17).

I really appreciate your efforts to improve the DOV.
Great job. 

When it comes to the fan speed control, though, I'm not entirely sure if Owon really messed that up, or if it was intentional—for example, to improve stability.
What do you guys think?

Thanks!
I still think it's a bug.
Here's why: the fan speed control service is running, and if you enable its logging, you can see that it monitors the internal sensor temperature and tries to adjust the speed, but nothing happens.
On top of that, there is a fan speed adjustment test in the device's service menu, and it doesn't work without my fix either.

The cooling issue itself is another story.
I absolutely dislike those blue thermal pads - their efficiency is very low, so I'll think about what to do with them.
In subsequent releases, Owon redesigned the heatsink - https://www.eevblog.com/forum/testgear/owon-ads824a-battery-option-question/

[Martin72]

In subsequent releases, Owon redesigned the heatsink

Apparently not just that one—in the pictures, you can see a board revision 1.1.1 instead of 1.0....

[TomC]

Hi,

The replacement unit arrived today—and, “of course,” has the same problem.
Counting Aldo's Scope, Lutz's, and mine (that makes two), there are now four units affected.
This is no longer a coincidence, but a systemic issue.
And when you measure the calibration output using the vertical setting—where the ripples appear—it looks even worse.
Good to know:
If you switch the coupling to GND, the problem goes away, so at least I have an idea of where to look.
It won't be easy.

Hi, I received your message.

My ADS824A doesn't seem to have that problem, see attachments. The main board photos are the best I have right now. The screenshots were taken with the scope running from the power brick that came with it. I had better results when noise is involved running from battery. Cheers!

[Martin72]

Thank you very much !

[Martin72]

I noticed on the “new” board that one IC isn't mounted anymore....Why...
The IC that isn't mounted anymore is also one of those “ST3SK” ones—I still don't know what type it is.
Hm-hm..

[KungFuJosh]

[Martin72]

I had actually considered removing the IC and setting up the 0-ohm jumpers as seen on the newer version.
But I would have liked to know beforehand what the circuit does—unfortunately, it’s covered by the heat sink, so I can’t measure it while it’s running.

[KungFuJosh]

I believe in you.

[Aldo22]

I had actually considered removing the IC and setting up the 0-ohm jumpers as seen on the newer version.
But I would have liked to know beforehand what the circuit does—unfortunately, it’s covered by the heat sink, so I can’t measure it while it’s running.

I'm sure you've also noticed that the the “A10” (if I'm reading that correctly) has been replaced with a "0" as well.

[Schenkenstein]

If you don't mind to try, I got a firmware update file from Owon. It works for the ADS800A and ADS900A with FW older than V1.0.1.0.17, I don't know about the Voltcraft but it should be the same.

Just copy the ota_update.zip to a memory stick (FAT32), plug it to the scope and open the App Center, it will show an update confirmation.

I've already tried it and it makes no difference regarding the ripple issue though.

I didn't test it further yet but one noticeable difference is regarding the cooling fan. Before, when the fan was spinning at low speeds it would make a very annoying whining noise, now it is fully on or off, no more speed control and the sound is louder.

Hi all,
Can someone please upload the firmware again? Unfortunately, the download link does not work anymore.

[Martin72]

Hi,

https://drive.google.com/file/d/1n_rpxFjv0Y_WHRd4dEcF8dl3q2oZ7MRm/view?usp=sharing

[Schenkenstein]

Hi,

https://drive.google.com/file/d/1n_rpxFjv0Y_WHRd4dEcF8dl3q2oZ7MRm/view?usp=sharing

Thank you!
Unfortunately, it seems that the update is not working with V1.0.1.0.13 which I have: the scope claims an 'error in the update package'. Guess, I have to upskill on Android hacking and get the update on there myself.

[Andi-61]

Hello, I had the same problem with the DOV1002. There wasn’t enough free storage space available. After freeing up some space, I was able to install the update. I also installed the Noctua fan. Thanks for the tips from the experts in the forum.

[Aldo22]

Hi,

https://drive.google.com/file/d/1n_rpxFjv0Y_WHRd4dEcF8dl3q2oZ7MRm/view?usp=sharing

Thank you!
Unfortunately, it seems that the update is not working with V1.0.1.0.13 which I have: the scope claims an 'error in the update package'. Guess, I have to upskill on Android hacking and get the update on there myself.

I compared Martin72's file with the first version of Microcheap.
The file size isn't exactly the same.
I don't know if that makes a difference, but I've uploaded the original version here for you again:
https://filebin.net/h4d7h6gn7lvep2fu

[Andi-61]

by the way, my DOV-1002 also has the ripple problem.

[Aldo22]

by the way, my DOV-1002 also has the ripple problem.

Thanks.
Do FFT and XY mode work perfectly for you with a higher memory depth?
I want to rule out the possibility that this is a general problem with the 2-channel versions.

[Martin72]

The file size isn't exactly the same.

I only had the unzipped version left, so I recompressed it.

[Martin72]

I had actually considered removing the IC and setting up the 0-ohm jumpers as seen on the newer version.
But I would have liked to know beforehand what the circuit does—unfortunately, it’s covered by the heat sink, so I can’t measure it while it’s running.

I couldn't stop thinking about it, so I followed the paths as far as the circuit allowed.
I still don't know exactly what the “ST3SK” does; maybe it's just an op-amp.
In any case, it was removed in the new revision—why...



The circuit on the Rev 1.0 board: a voltage reference may be buffered by the “ST3SK,” after which this 2.5V goes to the front end, where it powers a logic chip on each channel.
And I measured this 2.5V...
It's getting warmer...

[Microcheap]

I noticed on the “new” board that one IC isn't mounted anymore....Why...

Another difference is the added ceramic capacitor next to the relay. The value o resistor above the 0R jumper might be different as well but I can't see its value in the picture posted by TomC.

Hi all,
Can someone please upload the firmware again? Unfortunately, the download link does not work anymore.

I updated the link for the Firmware V1.0.1.0.17. It should not expire now. If you want to verify the file integrity after the download. Its checksum is SHA256: 58495913782f1dd00f343fefd281399664f18556501d0a0e1d1b47dd2653b544

This week I've contacted Owon that confirmed the small ripple in the 200mV range is a hardware issue and that they already fixed that in the later revisions. They offered me to replace my boards but I asked if there was a simple fix that I could do myself instead. I'm still awaiting for a reply, they are in the middle of a holiday in China now.

[Schenkenstein]

Hi,

https://drive.google.com/file/d/1n_rpxFjv0Y_WHRd4dEcF8dl3q2oZ7MRm/view?usp=sharing

Thank you!
Unfortunately, it seems that the update is not working with V1.0.1.0.13 which I have: the scope claims an 'error in the update package'. Guess, I have to upskill on Android hacking and get the update on there myself.

I compared Martin72's file with the first version of Microcheap.
The file size isn't exactly the same.
I don't know if that makes a difference, but I've uploaded the original version here for you again:
https://filebin.net/h4d7h6gn7lvep2fu

Thanks, this one worked like a charm!

[Martin72]

This week I've contacted Owon that confirmed the small ripple in the 200mV range is a hardware issue and that they already fixed that in the later revisions.

Well, you've already gotten further than I have—I haven't heard back yet.
It was kind of obvious that Owon had “quietly” fixed the issue and wouldn't be recalling the versions that had already been shipped.
The additional capacitor at the OP's output and the removal of the circuitry around the “ST3SK” chip are likely the measures taken to reduce ripple.
But it would be better to know for sure rather than just assume that's the case.
It would be great if I could get a close-up photo of the area with the additional capacitor near the IC, close to the relay...@TomC

[Schenkenstein]

I observed some weird behavior on channel 1 and 2 (but not 3 or 4): The scope measures about 1.25div too much (independent from V/div setting) when the current sample is exactly at the zero level (or thereabouts - I have not determined the exact value yet). I noticed it when I was playing around with the persistence which made those glitches apparent: with no signal applied, the glitches are not present when the vertical offset is below or above the zero div line. But as soon as the measurement noise makes it touch the horizontal line, it glitches like crazy (see images below). With an offset of 0.02div, its much lower and with 0.04div it's basically gone. I applied a sine and an offset to have it 'touch' the zero line in a controlled manner and it confirmed my suspicion that the glitches are related to a sample having a certain value - they only appear at the top of the sine wave where the samples are on the zero line but not as often as with the measurement noise only (probably due to the high resolution). Also, that behavior was only present with a high sample rate (>100MS/s) and without persistence, it's hard to notice. Did anyone observe something like that as well or do I have a bad ADC?