HP 5316B channel C issue

[gossamer]

Channel C on my unit doesnt work. So I started through the troubleshooting part of the service manual.
point 8-118 is fine, all voltages are present and correct.
8-119 is where it shows something is not right. So, Ive set the signal gen, 100Mhz, 280mVpp, 50Ohm output.
C1 measures 240mVpp and 100Mhz, at 0V offset. C2 measures the same. C3 signal is offset by 2.3v and measures the 100Mhz and 240mVpp. Now the manual shows (blurry scanned service manual, so hard to say), but signal looks the same as C1 and C2.
C4 I cant see anything apart from some high freq noise.

What I dont know now is whether U1 output is correct or not?