Agilent IC Chip Inside Scope

[bostonman]

Long shot, but I'm working on an Agilent 54831M scope and came across a section of the circuit that's different when comparing the two good channels to the two bad channels.

The two bad channels measure nearly identical to each other while the two good channels measure nearly identical to each other. I've traced the circuit and drew what I feel is a correct layout, however, it doesn't make any sense.

I've looked for information about the IC which is 1NB7-8477, but haven't found anything except it's an amplifier and some being sold on Ebay. Does anyone know if any information exists about this?

Attached is the circuit I've drawn that's essentially the circuit in question. R1 and C1 are two surface mount components that are not marked. I'm reluctant to remove the good ones and measure them, but I feel it may come down to that. C2, C3, and Z1 are also unmarked, but, if you look at my notes at the bottom, those points measure fine. Also, 'good' and 'bad' are referring to the good channels (Ch1 and C4) and the bad channels (Ch3 and Ch4).