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SDS1104X-E DC offset in AC coupling

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Deso:
Hi all,

I just joined the club of the SDS1104X-E owners. It replaced my good old DS1052E.
However, my joy lasted less than a minute until I spotted that there is a DC offset on all channels. I thought that it needs some time to get properly warm, so I left it for and more than 30 minutes (hours). BNCs started feel warm (39 C). DC offsets have improved but are not there yet. I switched to AC coupling and the DC offset became bigger. This behavior is also observed for the 4 channels. I ran the calibration (2 times) and the DC offset in DC coupling reset as it should. Switching to AC coupling shows a DC offset again. All the tests were performed without anything connected on the inputs, with connected and shorted probes and even with 50 ohm BNC terminator. No changes to the DC offsets in AC coupling.
I ran the very same tests with my old Rigol and there were no differences in the offset when switching between AC and DC coupling. Initially there was a large offset that was reset when the scope warmed up and didn't change for hours.
So my question is - is this a thing that I don't understand why it's happening, or is it a hardware issue?

Here are the scope details:
SW: 6.1.37R8
OS: 8.3
FPGA Ver: 2021-11-08
HW: 09-06

Thanks in advance

tautech:
Welcome to the forum.

Install 37R9 firmware.
https://int.siglent.com/upload_file/zip/firmware/Oscilloscope/SDS1xx4X-E_V6.1.37R9_EN.zip

Release note:
Fixed the problem: The skew of the two ADCs is not accuracy for hardware of 09 version (System Status shows Hardware Version: 09-xx). The other hardware version has no this problem.

Deso:
Thanks for the hint. I already updated the scope to 6.1.37R9. On cold scope and AC coupled channel it shows no DC offset. On DC coupling shows negative offset. After a few minutes the offset started to slowly increase to a positive values. I did another calibration as per the FW update instructions. It didn't help at all. Everything is as it was before the FW update. Even worse - the offsets became larger.

Ringmodulator:
Please perform the self-calibration routine after proper warm up and report back.

Regards
Chris

mwb1100:
And just in case: the probes should be disconnected when doing the self-calibration.

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