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Rigol DS2072 vertical problem

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battlecoder:
Hello all,
I bought a DS2072 oscilloscope in a "bundle" of assorted instruments from a fellow enthusiast. Everything was in working condition except a Rigol DS2072 scope that is having some issues.
The scope seems to be working mostly fine in almost every way, and the horizontal axis doesn't seem to present any problem. The vertical system, however, is where it's failing.


Both CH1 and CH2 have a "voltage" offset (this is both channels with no signal applied):


The offset changes with the vertical sensitivity setting, and with the position of the traces on the screen. The offset is exactly the same in AC and DC coupling modes.
If I move the traces to the center of the screen, however, the offset disappears. This happens in both channels:



The traces follow the screen position "correctly" when GND-coupled. They are drawn exactly at the trace level:


The vertical sensitivity is also off. This is supposed to be a 1Vpp wave, at 100mV/DIV (should be displayed with clipping):


The same 1Vpp wave, but at 500mV/DIV (should cover 2 divisions):



More details: I updated the firmware to the last available version (00.03.06) in case this was a software issue. Hardware version is 2.0. That did not help.
I have performed the self-calibration several times. With and without warm-up, and before and after the firmware update.
I also noticed that the scope had every "option" unlocked. In the System Info panel, for "model" it says "2202", and I assume this is due to the fact that it has the 200Mhz option too.
I don't need this scope to be 200Mhz, so if this, or any of the unlocked features is causing calibration issues I will more than happy to undo that, assuming it's possible. I have no idea what method was followed to unlock those options.

I also disassembled the scope to see if there any blown up component in either channels or the surrounding circuitry, but nothing seems burnt or damaged, "visually".

Any help would be greatly appreciated.

ebastler:
Have you tried a "factory reset"?
https://gotroot.ca/rigol/ds2000_factory_reset.pdf

battlecoder:

--- Quote from: ebastler on November 10, 2023, 06:17:31 am ---Have you tried a "factory reset"?
https://gotroot.ca/rigol/ds2000_factory_reset.pdf

--- End quote ---
Interesting. Just tried it. It beeped several times, and it definitely started in a different config than I left it on, but that unfortunately didn't fix the issue.
Thanks for the suggestion, though.

BlownUpCapacitor:
Capacitors. I had a similar problem in my Hantek and it just came down to some faulty capacitors filtering the supply voltage for the ADCs. The capacitors weren't allowing the proper voltage to power the ADCs. I knew this because I had a good Hantek scope that had different voltages. Replaced some caps and all was good after a self-cal. The capacitors had become conductive, which I found quite strange as they were MLCC types. But anything can happen with cheap parts I guess. I also found it odd that the PSU didn't trip.

However, this might not be the case for you but I think it's worth a try to go poking around with a probe to check the supply voltages and some capacitors.

ebastler:

--- Quote from: BlownUpCapacitor on November 11, 2023, 07:36:23 am ---Capacitors.

--- End quote ---

Your username suggests some perception bias, but yes, that is a plausible cause.  ;)

Without a second scope to compare with, it might be difficult to figure out which voltages are correct though. There is a "service guide" from Rigol, but it does not go beyond disassembly instructions: https://www.manualslib.com/manual/1543054/Rigol-Ds2000-Series.html. So, as you suggested, probing around and looking for implausible voltages or capacitance values is probably the only way to go.

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