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Rigol DG2052 making a screenshot and possible firmware hack

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tv84:

--- Quote from: JimKnopf on January 28, 2023, 05:33:23 pm ---How can i write to usb device in uboot?
Steps are not well documented and rarely used in this forum.

--- End quote ---

That depends on the uboot implementation. It's not a generic thing.

Have you looked at all the commands available in uboot?

Alternatively, you can always dump your mem contents to screen (in hex form, for example) and log it in your terminal client. Then, in the PC, you just parse the output and create a bin file. I've done it dozens of times.

Many times uboot USB can't see the partitions and you only see the device. In that case, you must consider writing/reading to the direct raw sectors of the USB device.

Njk:
The instrument integrates the frequency counter. Similar to that in DG800/900 series, it has the two input couplings, DC and AC. There is at least one confirmed report in the sister thread about the AC coupling issue. When coupling is set to "AC", the center pin of the BNC input connector of the counter is internally tied to -5.3 V voltage level by a high ohm resistor https://www.eevblog.com/forum/testgear/new-rigol-16-bit-function-generators-dg800900-series/msg3591372/#msg3591372. That seems unusual and I wonder if DG2000 is also affected.

According to Rigol, both DG2000 and DG900 series uses essentially similar HW. But let's look at the frequency counter areas of the DG2000 and DG800 PCBs (attached). The difference is not only in the layouts. In both the designs, the input signal from the connector is first routed to the clamping diode array (a SOT-23 part with JY marking, likely BAV199). Concerning the DC path, the signal is then passes through the resistor of 88 (or 66) Ohm. Then there is a switch that is likely related to the AC/DC coupling. That's where the difference is.

In the DG800, the switch is made of the two SOT-23 parts (with 61U and 6K markings, likely old Fairchild JFETs MMBF5461 and MMBF4392 respectively. Perhaps -5.3 V is a bias voltage for the JFETs, so user must bring his own cap for AC coupling). While in the DG2000, the switch is made of single big part, the marking of which is difficult to read. So the analog front ends are apparently different, and the reason is not clear.

Perhaps it's a minor change because of the parts availability. DG2000 was designed later, and in 2019-2020 both MMBF5461 and MMBF4392 were declared obsolete by OnSemi. While MMBF4392 was replaced with MMBF4392L, no substitution was offered for MMBF5461, so Rigol was forced to change the design. The chances are a later DG800/900 HW revisions were also updated accordingly (pure speculation). That's why it's interesting if the AC coupling issue is related only to the old design or not.

All in all, there is a lot of components in the counter PCB area. Dozens of discrete components and 8 op-amps in total. No idea if every the op-amp is related to the frequency counter, but there is also one 1P8T analog switch (HC4051) the purpose of which is not clear. There is only one that part so it's unlikely it's used elsewhere (as the generator has two channels). It's quite complex electrical arrangement for the frequency counter of unspecified accuracy. Moreover, there is a dedicated 16-bit DAC and two fast comparators. With one more DAC, it could be possible to implement two independent triggers, like in more serious counters, allowing to measure e.g. a pulse edge time. But it seems there are too many stoppers in the SW department.

P.S. JimKnopf, thanks for the hi-res PCB images. Hope you're doing well.

JimKnopf:
@NjK

I just tested the counter voltage in DC and AC coupling mode.
I didn't measure negative voltage like -5,x V on center pin. There is no difference between DC and AC coupling.
The AC measurement showing me some normal fluctuating voltage.

I grabbed some scrrenshots from linux terminal using
  echo "HCOPy:SDUMp:DATA:Format PNG" | nc -w1 192.168.10.54 5555
  echo ":DISPLAY:DATA? 0" | nc -w1 192.168.10.54 5555  | dd bs=1 skip=11 of=counter_1.png (or whatever name you want)
  (don't forget to unlock the screen after using SCPI commands by pressing Shift and then Arb|Help/Local button on DG2052).

I'm running Software Version 00.02.06.00.01 on my DG2052.

Activating the counter disables Output 2 (normal behavior, i remember that i read something in the manual about that).
The Counter button LED is flashing when activated instead of the permanent glow like Output 1 and 2 button.

 

TurboTom:
The signal path of the counter circuitry is basically only rounted through discretes (except for final digitization that is). There's a jfet input and some level shifting taking place. @Njk is correct --  the AC/DC switching is arranged diffenetly in the two models, a look at Rigol's most inexpensive oscilloscopes helps here: The SO4 component used in the DG2000 circuitry is a Cosmo solid state (PhotoMOS) relay, used to short out the coupling cap. Since apparently a perfect galvanic isolation from control to signal paths isn't required (which may affect signal fidelity), the older circuitry utilizes here a cheaper, discrete approach.

The TL072 that's apparently routed in the counter's signal path is most likely processing the DC/LF channel of the input amplifier and maybe providing some bias voltages. The signal is then routed through the relay (later more on that) to the LMH7322 comparator (QFN24 with the markings lasered off in the DG800 version) that finally digitizes the counter input signal and feeds it differentially to the FPGA.

The small TSOP8 (DAC8560), the TL072 and TL074 opamps and the 4051 analog multiplexer (sample&hold) are just used to provide several high-resolution (16 bit) analog control voltages to the rest of the circuitry (channel offsets, trigger levels and who knows what). This circuitry block can be found in many Rigol and Siglent AWGs with almost exactly the same components, and even DSOs feature this circuitry.

One detail that's most peculiar and not 100% clear to me is why the AWG pre-driver outputs are routed back to the analog comparator'inputs (via 499R - 68A marking) and (probably) 10kR pullups/grounding resistors. This feedback signal is multiplexed via the relay with the counter input channel, and that's the reason the DG800/900/2000 series of AWGs unfortunately loses one of its AWG channels whenever the counter is enabled. The additionally required fast comparator fell victim to the "bean counters" in these economy AWGs...  Maybe the AWG signal feedback is somewhat related to propagation delay compensation/deskew of the channels?

Njk:

--- Quote from: JimKnopf on May 29, 2023, 09:49:09 am ---I didn't measure negative voltage like -5,x V on center pin. There is no difference between DC and AC coupling.

--- End quote ---
So another HW difference between DG2000 and DG800/900 is finally revealed. BTW, it seems in DG800 the negative bias produces the two effects. First, it can be measured on the center pin. Second, it affects the comparator. Looks like with AC coupling, the virtual zero level is also biased down to at least -2.5 V and the counter shows nothing unless the trigger level is set to -2.5 V. Even after that, the sensitivity is much worse than with DC coupling, suggesting the virtual ground is actually biased to a deeper minus level, to -5V. Looks like AC coupling is implemented just to check the box. It must be better in DG2000, I presume.

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