DSO4254B channel 2 damaged?

[Betto_EEV]

Hi everyone!
I've bought this DSO and I've discovered a problem on channel 2.
With ch1, ch2 and ch3 connected  on 2Vpp/1kHz square wave I get on ch2 an offset [5V/div].
If I decrease volt/div I no longer see the waveform on ch2. It goes off screen at the top.

I have already swapped several components in this order between channel 2 and 3 but the problem remained on channel 2[see SwitchedParts.png].

• 1. 6552
• 2. ad8510
• 3. ad8370
• 4. 3 MMBTH10 marked 3em
• 5. PMBF4393 marked w6g

I have access to the serial interface but I don't know what to check.

Then I've found a difference in Offset_details.png area.
Here I get:
ch1 -2,379v
ch2 -2,328v
ch3 -2,373v
ch4 -2,362v

Going backwards from this area I arrived at a Hex inverter (?!?) And touching the L1302 inductor with the multimeter in Volt mode, the waveform goes up (offset upwards).

any idea how to fix?

[Betto_EEV]

when I apply a voltage across the resistance indicated by the blue arrow, the waveform lowers on the screen thus reducing the vertical offset on channel 2.
This resistor is connected at the output of Hex Inverter [U33] on top left of image.
The input appears to come from an inductor that ends up on the FPGA

[Betto_EEV]

I finally found the solution !!
I reversed the feedback resistor between channel 2 and 3[806k on bottom left corner of IC n.3 in SwitchedParts.png].
Channel 2 now has a stable signal with no oscillations.
I think the problem was due to a dirty weld.

Performed a correct calibration without errors (now the signal on channel 2 during the calibration was easily aligned with the other 3 channels).

Hope it can help someone with a similar problem.