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KeithRussell

I think it's broken

Question

I have an AD2 that I use a lot and today the Channel 1 started showing an input voltage of -21 with nothing connected. Channel 2 and all other functions work great.

I restarted the computer, updated the software, and power cycled the AD2. No change.

I calibrated the waveform generator and then the scope, but scope calibration failed saying that Channel 1 is showing too high on the input when grounded. I tried reverting to the factory calibration, but the symptoms remained the same.

So, is it truly broken? If so, is there a way to repair it?

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You were correct, attila, it was the mux. After confirming with measurements, I cut pins 10 and 15 to be double-sure it wasn't the buffer. 

I'm ordering anther ADG612 now.

After going over all my measurements and checking everything I did, I am confident that I did not damage the mux. I don't have anything over 9 volts on the bench, and I did not have a mis-matched ground problem anywhere. It just died of its own accord.

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Hello.

 

Mr Attila AKA "Technical Forum Moderator".

 

I think i have the same problem as Mr Russell.

 

My AD2 will not go down from +20 volts. I was doing some measurements with a transformer and the BNC kit for the AD2 and after some measurements, it looks like I also broke my Channel 2 input. The probes were x10 in the attenuation department.

 

Will the solution suggested work also for me?     I have almost the same issue but  is not -21, is +21.

 

The device works well measuring frequencies, the attached image shows the generator connected to channel 2, measuring 10 MHz.

 

Discovery BNC.jpg

Scope and WFG 10 MHz.pdf

Edited by Camarillo
There. Had to convert the image to PDF for it to be uploaded.

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Sorry, forgot to add the MHz part.

 

 

Edit: can´t upload the other picture.

 

 

EDIT: I was able to upload the picture but as a PDF.

Edited by Camarillo
Was now able to upload a file now.

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Hi @Camarillo

Probably some high voltage transient input or accidentally having the probe at 1x with high voltage damaged the ADG612.

Before replacing the ADG612 you could verify the VREF_SC2 and VOFF_SC2 voltages.
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#scope_reference_and_offset
- the VREF should be about 2V
- the VOFF with:
   0V offset about 2V
   +2.5V offset with 500mV/div range about 3V, like the screenshot below
   --2.5V offset with 500mV/div range about 1V

image.png.a00584b5160cef32772b63eb85250b7c.pngimage.thumb.png.c933264f586dbf022bc47d05ea4ad2ee.png

image.png.3de50a2b06179d2025c158b39c774c97.png

Some further troubleshooting posts:

 

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Hello Mr Attila.

 

I think I did the measurements but not sure if I did them in the right manner.

 

My setup:

-OSC1  ---->  GND

+OSC1 ----> to test points

 

Did all measurements with respect to GND of the AD2. In the last measurement I remembered that it also could have been differential measurements.  Did all the differential measurements and the result is the same with the other two with respect to GND of the AD2.

 

I had to modify the +2.5 offset with 0.5 scale because the measurement will not show it self (higher than 0 volts I guess).

 

 

 

This was the VREF_SC2, with respect to GND it was close to 2 volts.
This was the VREF_SC2, with respect to GND it was close to 2 volts.

 

 

 

This one is the NETC410_1 with respect to GND. It was 1.1947v

This one is the NETC410_1 with respect to GND. It was 1.1947v

 

 

 

This one is the diferential measurement, just took it after I´ve finished...

Differential measurement

 

 

 

This one is the VOFF with 0 volts offset. It was almost 2 volts (1.9969)

 1293762275_VOFFwith0voffset.thumb.png.635f90e4910090433fa6bfe4f3f5a3fe.png

 

 

 

This one is NET409_1 with 0 volts Offset respect to GND. It was 0.5855 volts.

1288373568_NETC409_1with0voffset.thumb.png.e7d38142b4e931f3e8cac3e34e0965e7.png

 

 

 

 

This one is VOFF with -2.5 volts offset and 0.5 volts/div.   It measures 1.99 volts.

1774759781_VOFFwith-2_5voffset.thumb.png.c1ab770d40ae142210ef37ddcc08491c.png

 

 

 

 

 

This one is NETC409_1 with -2.5 volts offset with 0.5 volts/div.   It measures 0.5786 volts.

711512169_NETC409_1with-2_5voffset.thumb.png.ac0db5de5baed8ba2cf495652a143de6.png

 

 

 

 

 

 

VREF_SC2.png

NETC410_1.png

VREF_SC2 and NET410_1 Differential.png

VOFF with 0v offset.png

NETC409_1 with 0v offset.png

VOFF with -2_5v offset.png

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I´m sorry with all those uploads. Don´t know what I did but apparently I uploaded all the files again.

 

 

The last two measurements:

 

 

This one is the +2.5 Offset at VOFF.  I had to modify the range from 0.5 to 1 volt/div.  It measures 2 volts.

2018914504_VOFFwith2_5voffset.thumb.png.6037e7c5d80eb236d52b49038c30c1cd.png

 

 

 

This one is the NET409_1 with +2.5 volts offset.  I left the same 1 volt/div as the other one. It measures 0.5959 volts.

1466025298_NETC409_1with2_5voffset.thumb.png.cf8c0fdc88777fe93b0557a840b13ce4.png

 

 

 

What do you think?  Could the MUX be the problem?

 

 

Thank you so very much.

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Hi @Camarillo

I meant measuring the VOFF_SC2 relative to the device GND with external DMM.
Having the scope channel 2 range 500mV/div or lower, changing the offset between -2.5V and 2.5V should change the VOFF_SC2 between ~1V and ~3V
Above 500mV/div for offset between -25V and +25V change VOFF between ~1V and ~3V.

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On 2/20/2020 at 1:47 AM, attila said:

Hi @Camarillo

I meant measuring the VOFF_SC2 relative to the device GND with external DMM.
Having the scope channel 2 range 500mV/div or lower, changing the offset between -2.5V and 2.5V should change the VOFF_SC2 between ~1V and ~3V
Above 500mV/div for offset between -25V and +25V change VOFF between ~1V and ~3V.

Oh.... sorry, did not understad that.

 

Did the measurements. They are within range:

VREF2V = 0V

VOFF_SC2 with 0V offset = 1.94V,

VOFF_SC2 with 2.5V offset = 2.99V

VOFF_SC2 with -2.5V offset = 1.01V

 

All measurementes respecto to the device´s ground and with 500mV/Div for channel 2.

Edited by Camarillo
Definded the voltages.

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Hi @Camarillo

According your measurements the offset DAC is working.

I almost forgot that odd reading or output offset could be due to wrong calibration.
Since the offset voltage is applied this it likely good, but please perform a "Load factory" and see the oscilloscope readings again to make sure the calibration is not culprit.
image.png.836e5bac88b6373624ad01844fe04d8e.png

Otherwise the 21V reading is likely due to damaged ADG612.
The one for channel 2 is on the right side, the 16pin IC above the trimmers.

 

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Thanks for the reply.

 

Did the factory reset but the measurementes were the same. Although something happended that I did not notice: if I start channel 2 with the 500mV/Div, if i change it to 5V/Div, the signal from channel 2 goes to -3V and after a few seconds, it goes to +21 (with nothing conected to the probes).

 

Did a calibration after loading the factory data. The waveform channel, both 1 and 2 passed. But the oscilloscope did not, and it showed the behaviour described above (-2.7 volts to +21 volts.

 

Do you think it might be the MUX ADG612?

 

Thanks.

 

 

 

image.png

Edited by Camarillo
Deleted the same image. Uploaded it twice.

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Hi @Camarillo

It is most probably the C2 ADG612 damaged, the first IC in the input path.

The 2.7v is the maximum input reading with high gain, <= 500mV/div

Sorry for the late reply, I'm off work this week.

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On 2/27/2020 at 1:30 AM, attila said:

Hi @Camarillo

It is most probably the C2 ADG612 damaged, the first IC in the input path. 

Hello. 

Thanks for the info. 

 

Just one question, and this might be very transparent for everyone but me:

Which of the two ADG612 is the channel 2?

 

I have all the intention to do that repair in this week. Good thing I have the AD1 for testing. 

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At the time of your response, I was looking at this other of your responses: 

 

Was looking for those resistors IDs in the reference document to determine which one was Channel 2.

 

 

Thanks, I´ll now proceed to operate 😈

 

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Hi again......

 

I think I broke it for sure now.

 

 

This image is with the wave generator #1 with its output at 5 volts with no offset.

image.thumb.png.c24917eff8826b7a3413d590f3bf2994.png

 

 

 

After resoldering the ADG612, Channel two was able to mirror the information in channel one.

image.thumb.png.29e523d33dcd2d8e2ffd2a7efd02da6a.png

 

 

 

Here are both channels at the same time.

image.thumb.png.313d71c3562581754677ab2efa994da9.png

 

 

 

It´s strange because Channel one was not failing. Maybe it´s because my soldering skills with SMD is not that good. I just soldered the IC.

Maybe I broke it for sure now.

 

 

Did a device calibration setup and the first  two steps generate -5.05 volts. (it says demo mode but the measurements were made before disconnecting the device)

image.thumb.png.ac53cb08fc6359dff374e08720beaa5e.png

 

 

 

Right now I don´t have access to my AD1. Next week I´ll have access to it and will use it as a reference to measure analog signals.

 

Can you provide some insight?

 

 

Thanks.

 

 

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Hi @Camarillo

You have fixed the oscilloscope, but it looks like the AWG output is damaged too :(

You can verify the following rails, when the device is connected and opened with WaveForms, between the no load component pads and device ground.
Bottom left edge of the board:

image.png.75b5806e352defdeff0fa5e687917f48.png

 

In the following post you have further troubleshooting:

 

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