Analog Discovery 2 probe calibration issue

[manymiles5]

I am a hobbyist, new to oscilloscopes.  I recently purchased the Analog Discovery 2, the BNC Adapter and the BNC Oscilloscope 1X/10X Probe pair.

I've read this post and this post, and followed this video on calibration, but, I'm not sure the AD2 and/or the probes are measuring properly or not.  I cannot get square off the signals.  The screenshots indicate the maximum I am able to deflect the signal when rotating the screw within the probes.  From my understanding, rotating the screws in the probes should make the signals become square.

Here's other information which may be indiscernible in the attachments, which may or may not be relevant (cuz I'm a noob).

• Both probes have the 1X/10X switch set to 10X
• The probes are both clipped to the W1 pin on the BNC Adapter board
• Both probes have their ground clip connected to one (and the same) of the flywire ground pins
• Both probes are set to DC Coupling on the adapter board
• JP4 and JP5 on the adapter board are set to 50 Ohm, though I don't think that matters because I'm not actually using the Waveform connectors on the adapter board
• In the screenshots, the channels are configured for "Attenuation: 1X" within the Waveforms software, but, a similar non-squareness occurs when set to "10 X"
• I'm using Waveforms 3.12.2 64-bit Qt5.6.3 on Ubuntu 18.04.4
• The AD2 is connected to a USB3 port, directly attached to the computer (no USB hub)

Any advice and/or guidance would be greatly appreciated, especially considering I may have missed something that would be obvious to an advanced user.

[attila]

Hi @manymiles5

The probes look to be faulty or at least not in the specs.
For warranty and replacement please contact support dot digilent at ni dot com 
They will need your name, when you purchased the device, whom you purchased it from (i.e. Digilent or a distributor), and the serial number on the underside of the device. If you purchased the board from a distributor, you will need to contact them about their warranty.

[attila]

Hi @manymiles5

It looks like it is undercompensated. Try adjusting the probe trimmers.

https://forum.digilentinc.com/topic/4227-discovery-bnc-scope-distortion/?do=findComment&comment=16445

 

[manymiles5]

Thanks for the speedy response.

I've rotated both trimmers through more than 360 degrees.  When I do that, the readings only get as high as 176 mV on Channel 1 and 141 mV on Channel 2 before they start to reduce again.  (I *think* they are supposed to get REALLY close to 200 mV, right?)  (Note that I've included those readings in the Y Cursors window)

 

[attila]

Hi @manymiles5

Did you get P6100 probes?
Your probes look a bit different than the ones I have.
It may be different brand or version, with different adjustment range...

With these I can adjust the compensation with the following limits:

[manymiles5]

Yes, I have the P6100 probes.

[manymiles5]

And I am not able to obtain the readings you did by twisting the trimmer.  It never goes above 3.3V.

 

I've now tried it on two different computers (both using Ubuntu 18.04.4)

[attila]

Hi @manymiles5

To have higher voltage set higher Amplitude in Wavegen.

[manymiles5]

I already had it set to 4V

[manymiles5]

Ok, will do.

I very much appreciate the speedy and attentive response.  Thanks a bunch, @attila!!

[manymiles5]

@attila,

I just received the replacement probes from DigiKey.  They work as expected, so, you suspicion that the other probes were faulty was correct.

Thanks for the help!

 

[JamieRI]

@manymiles5 How did you get your probes replaced? I could have written your thread, as my best probe compensation looks like the undercompensated images ni your picture. I also I purchased my probes from Digikey on July 1, 2020.  https://www.digikey.com/products/en?keywords=1286-1075-ND

Thank you!

Jamie

[JColvin]

Hi @JamieRI,

If you bought them from Digikey, you would need to contact Digikey directly about a replacement (Digikey will then contact Digilent separately). I do not know Digikey's RMA policy though with regards to time frame, but feel free to reference this thread regarding the probe calibration.

Thanks,
JColvin

[JamieRI]

58 minutes ago, JColvin said:

Hi @JamieRI,

If you bought them from Digikey, you would need to contact Digikey directly about a replacement (Digikey will then contact Digilent separately). I do not know Digikey's RMA policy though with regards to time frame, but feel free to reference this thread regarding the probe calibration.

Thanks,
JColvin

Thank you, I am writing to Digikey hoping they will take them back after 3 months. They are now out of stock. Is there another option that will compensate for the 24 pF inputs?

[JColvin]

Hi @JamieRI,

I am personally not familiar with other probe options, but @attila might have an alternate suggestion.

Thanks,
JColvin

[attila]

Hi @JamieRI

The Digilent probes are now in stock:
https://www.digikey.com/en/products/detail/digilent-inc/460-004/4840870

If you want to purchase other probes you should choose one with compensation range above 22-24pF. I hope the declared value is valid.

https://www.digikey.com/en/products/filter/test-leads-oscilloscope-probes/629?s=N4IgjCBcpgHAzFUBjKAzAhgGwM4FMAaEAeygG0R5YAWANgE4Ij4BWABmoRGYHZae%2BIALpEADgBcoIAMriATgEsAdgHMQAX2bwI0EKkiZchEuRC14nesLGTIM%2BcrWaQAWgBMSPVHkBXY6UgKFmsQCSkNZw9A0LliACM8ENpPBQATKRcwNiZQ2xBuEHEAT1FEuwwcVHV1IA