MPO6204D - measurement error after firmware update

mepavel

Hello!
I purchased an MPO6204D oscilloscope. The factory version of the firmware and the serial number in the photo are attached to the post.
After updating the firmware to the current version "dso6kb_func_210210" on all CH1-CH4 channels, a measurement error occurred by about - (10 ... 12)%. For example, 1 V is applied to the input, and 900 mV is measured. In this case, both signal generators provide an accurate voltage, which is confirmed by an external digital multimeter. I tried to self-calibrate several times, but it doesn't help. With the factory firmware, everything fit into an error of 1%.
As it turned out, the measured voltage at the analog inputs CH1-CH4 is underestimated by 10-12% only when one channel is active. If you make 2 or more channels active, then the measurement error disappears.
Attached a demo video about this issue: https://disk.yandex.ru/i/eXeYY_bV1uPRpg
The video shows that the swing of the output sinusoidal voltage of the generator is set: 1.414 Vpp. When one channel CH1 is active, DVM shows 451 mVrms, although it should be 500 mVrms. After activating additional channels, the error disappears and DVM shows 498 mVrms. The oscillogram shows that the voltage swing of the test signal increases to a correct value when 2 or more channels are activated.
If you make channels 1, 3 and 4 active, then the measured value, on the contrary, increases to 530 mVrms.
Please help solve this problem.
Is it possible to somehow return the factory firmware?
Respectfully yours, Pavel!

Jing

Sorry, this range of yours is not accurate because there is no accurate calibration when leaving the factory. If you want to correct this error, you can repair it.