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Analog Discovery WaveForm Generator Failure


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Hi,

First, The Analog Discovery 2 is a very handy device and i am very pleased with all the functionality it offers.

I got a problem with my device. The channel one of the wave form generator is not working any more. Here is the full the story. i mixed up the scopes for the signal generator and the oscilloscope and i ended up trying to measure a voltage of about 80v with the scope connected to waveform generator. As a result the device disconnected from my laptop. I noticed my mistake, unplugged the scope and tried to reconnect the device. It does show up in the list of available devices with all values of the register, S/N, state... But once i have clicked on 'select', an error pops with 'communication with the device failed'. I connected an external power supply to Analog D and this device can now be connected to Waveform (?!). If I try to set a sinusoidal signal on the channel one of the waveform generator, it shows either a clipped signal or absolutely nothing depending on the Vpp voltage. Also, their is a spurious 3V drop between ground and the output of the channel 1 To finish, the device warms up very quickely.


Does anyone has an idea how to fix that ? To be honnest, i have made an huge mix-take with the device, do you think that someone at Digilent will agree to have look at the device ?

Edit: Waveform indicates a consumption of 800mA / 4.8V on the AUX power supply, the temp is around 50 °C. Also there is a sound emitted by the device when connected, like a whistling.
Best Regards,

Nicolas

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Hi Nicolas,

I’m sorry to hear that. Unfortunately, we also don’t have the resources (tools and technicians) to repair the broken boards.

Even if you didn’t make the mistake to connect the wave-gen with the scope and everything was wired up correctly, you would’ve ended burning your device because Analog Discovery 2 is not capable of measuring 80V, its limit being 50V. Since this isn't a manufacturing defect, it is also not covered by warranty so we can't replace it.

I’m sorry we can’t help more.

Best regards,

Bianca

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Yeah, I know it is on me.


But I usually do not give up easily. Here is my trouble shooting.

I have managed to spot a short circuit on the output stage of the AWG1 caused by a fried op amp, i changed it and the consumption is now back to a std level (300mA), the board can now be connected to my laptop without power supply.


The AWG1 generates a wave, but there are two problems.

There is, as already mentioned, an offset and i can not correct it by calibration of the high gain AWG1. Also, the spectral behaviour changed : there is a loss in the generation of the wave, if i select one volt for the peak to peak voltage, the amplitude of the effectively generated wave decreased as the frequency increased, there is a low pass filter somewhere.

I insist : this offset appears only on the High Gain Calibration procedures and also on the scope.

The I/V stage : The Audio works fine! No problem! No loss at high gain frequency. So the generation of the wave is ok nothing bad append to the DAC. The AD8068 is a dual op amp, the figure 19 of the documentation is missing, is the Right Audio circuit and the out circuit of the AWG1 use separate op amp ?

Could you provide me the Figure 19 . This would be priceless for me.

Also :  The offset is provided by a chip AD5645R which also provides voltage for the on board power supply, the latter work well.

Best Regards,

Nicolas

 

 

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Verify the AWG1V2_REF, which should be 1.2V, and the AWG1/2_REF should be 1V
These are located on the bottom of the board.

IC13 is above the right side of connector soldering:

i3.thumb.png.cc5f5fb1c859e0e76f72c9f2390b0e04.png

 

IC42 above IC13:

i4.png.30475f75c89e60508a160ca50e9c42f8.png

 

Verify the +/- 3.3/5.5V

IC15 is on the right side of TxDAC

i2.thumb.png.08412f36feb40e739cb04aae63236216.png

 

IC16 is on the lower edge, under the header, almost in the middle:

i1.thumb.png.a4a4b345085eacb78efcb772f3d62b51.png

 

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Hi @attila,

Thanks for the figure and the typons ! Your are right there is a problem with caching. I will test the voltage you mentioned during the next days. I have checked the output of the Audio on my scope, everything is ok. I think that the Feedback capacitor C163 may have been damaged causing the cut off frequency of the RC cell to have moved. I will check.

 

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Hi attila.

i am trying to troubleshoot on some "broken" AD2's. browsing through all sorts off semi related forums etc. i found this thread. i work at university of Aarhus, Denmark in the department of  electronics engineering and the AD2's are used a lot in our education. but now and then student are "torturing" the devices and my job is to either repair them or to asses if it is a warranty case. 

often the i try to do the calibration wizard to get a hint of what's wrong. and i often i get the same error. when i get to typing in the measured values for wavegen 1 i get stuck with the -5 V measurment because it shows - 0.714 ish volts and the wizard are not able to proceed. that is why i found you test interesting and thought i simple check of reference voltages might reveal something. but when i measure the points in your description i do get all the right voltages except the "AWG1/2_REF should be 1V" (as i understand as two seperate points that should read the same voltage. AWG1_REF and AWG2_REF.) these both read 1.2 volts. Am i understanding this right. that this should be two seperate points? if yes does it tell you something that AWG1/2_REF is 1.2 volts and not 1 volt? 

regards Søren

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Hi @sbrun

The 1.2V for VREF_AWG1/2 (VREF1V2_AWG) is correct. The REFIO (VREF1V_AWG) for the DAC should be 1V.
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#awg_reference_and_offset

Probably the output amp is damaged. Here you can see this IC16:
https://reference.digilentinc.com/analog_discovery_2/refmanual#figure_19

image.thumb.png.e91ba93fb52a302711f21c4c7825bde0.png

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I'm repairing AD2's for the University of Helsinki (Electronics research lab). We are using the impedance adapter to measure capacitive ultrasound transducers. I now have diagnosed four AD2's with burnt out amplifier on W1. Are we doing something wrong when they keep breaking?

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Hi @tpaulin

The AWG outputs are protected with PTC in the output amplifier loop:
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#awg_iv 

The AWG outputs should not be connected/shorted with other outputs.
It is protected for rails up to +/-5V, but it could survive miss-connection to higher 10-15V rails too.

Could you proved more info about the experiment?

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Hi @attila

We have the AD2 connected through the impedance analyzer adapter to high power ultrasonic transducers (20-30kHz, piezo stacks). We measure the resonant frequency of these with mechanical stress. Sometimes also through an impedance matching circuit consisting of transformers and chokes. I'm thinking that the piezos might generate voltage spikes? We have also destroyed the multiplexer on channel 2 on several occasions.

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Hi @tpaulin

Sorry to hear this. I think you could use some zenner diodes to protect the device.

Even a simple piezo tape can generate high voltage that could damage electronics.
Are you referring to Scope channel 2 switch/mux ?
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#scope_input_divider_and_gain_selection

image.thumb.png.7ca14da09e80c4f1edeecbd2618a4a10.png

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