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Hantek 2000 series - 2C42/2C72/2D42/2D72
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gf:

--- Quote from: mostorer on April 07, 2020, 09:22:53 pm ---Yes, you are right but, to be a simmetrical diff amplifier as I also supposed (as also suggested on ADC902E datasheet) I should have to find a resistor from U13.3 to gnd. Not being able to find it.

--- End quote ---

The 560 Ohm resistor (marked "561") on the left side of my AWG-AMP.jpg photo, below the two 150 Ohm resistors (marked "18A").
mostorer:
Sure, how did I not see it? It is already of the correct value.

Thanks
mostorer:

--- Quote from: gf on April 07, 2020, 07:15:30 pm ---Is everything related to the AWG populated as in a geniune 2D72?

Are the various 0 Ohm resistors replaced with the actual values as well?

Are the 49.9 Ohm (68X) resistors from the DAC outputs to GND present?

What DC voltage do you measure from DAC pin 17 to GND, and from pin 18 to GND?

What is the value of your Rset resistor, from DAC pin 18 to GND?

When you set the AWG to rectangle with amplitude=2.5V and offset=0V, what peak-to-peak voltages do you measure on the two DAC outputs?
Expected are about 500mVpp on one output, and about 850mVpp on the other one.

--- End quote ---

Hi gf, check done!

So, first of all I can say that all 0 ohm resistors were replaced as requested and now are exactly the same as in your pictures.
That implies that also 68X resistors from DAC outputs to GND are there.

Moving to measures, pin 17 to GND is 1.247V wile 18 to GND 1.243V. From DAC902E datasheet pin 17 (REF in) should be 1.24 so, considering voltmeter tolerance, sounds good.
Rset was already in place, and is a 1.78K (25B), the same as in your 2d72.

Now, set AWG square wave, amp 2.5V with offset 0, on DAC outputs I have 700mVpp and 1100mVpp. They seems a little too much based on what you wrote.

In any case, let's wait the coax cable to make final testing, after replacing feedback resistor on U13, that is now 560 ohm as it should.

Regards, mostorer
gf:
The numbers look pretty reasonable. The Chinese DAC in in the genuine 2D72 has a lower vref than the DAC902 - only  about 1.1V instead of 1.24V. Consequently, in order to source the same output current, a larger Rset value is required for the DAC902. Likely the calibration can still fix the difference, but keep in mind that a full-scale output current of 22.3mA (= 1.24V / 1.78kOhm * 32) already exceeds the DAC902's upper limit of 20mA. So it is certainly not wrong to increase Rset to 2kOhm, which will reduce the DAC output currents (and voltages) by about 10% then. Given your measured DAC output voltages, even Rset=2.2k may happen to yield just enough output current, but that's very close to the limit then, leaving almost no headroom for tolerances (the calibration can only down-scale the digital counts sent to the DAC, but it cannot up-scale them to a value beyond 2^12-1).

Instead of a coax cable, the probe in 1x setting might work as well if you manage to avoid a loose contact for the duration of the calibration. Btw, don't forget to auto-calibrate the scope first before you calibrate the AWG. IMO it were better if they had used the DMM for the AWG calibration, instead of the scope, since the DMM is more accurate. But well, they didn't - maybe because it would require a BNC to banana cable :-//

gf
mostorer:
BNC cable arrived, so I'm going to calibrate the AWG.

First of all I have uploaded into the scope the formware HantekHTX2019031201.dfu published previously in this forum.
As already written in my previous post, screen upside-down with white background.
Run the general calibration from the main menu, then connected the BNC-BNC cable and run the AWG calibration.

Calibration success !!!

Going to scope screen, the sinusoid is perfectly tuned 600mV -600mV, perfectly centered (offset 0).
At this point I update the firmware with the last dfu available, but when I swith the scope on, I have a big surprise ... the AWG is not calibrated.

It seems that the firmware update reset calibration, or the old calibration firmware does not save the calibration data at all.

Any trick to maintain calibration with up-to-date firmware ?

mostorer
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