Agilent 54624A CH2 out of calibration

[mr_rock]

Hello everyone - I have an Agilent 54624A oscilloscope that had been working fine for me for a while now, but Ch 2 is now wonky.  Feeding the same signal into ch 1 and ch 2 and doing an auto-scale sets to two channels differently.

CH1 CH2.jpg

If I do the same with ch 1 and ch 3, they are the same, same with ch 1 and ch 4.

CH1 CH3.jpg

I tried running a self-calibration, which failed on ch 2, leaving the status as:

Stats.jpg

I have gone though manually setting ch 2 and it acts the same. I have verified the probe attenuation setting is the same for both channels.  I have the service manual - such as it is - which is quite limited, and offers no calibration / adjustment beyond running the self-calibration.

As three of the four channels check out as good, I could just ignore ch 2, but I'd rather they were all working. If I can fix this myself, that would be my preference, but I'm not sure where to look next. 

Open to any suggestions.