Come back after findings from the manufacturer answers.
Did you follow the traces to the absent IC to check if has to do with external/internal battery operation circuitry option ? Post a sketch of the circuitry traced from observation.
from Circuit position the IC function could be a RF amplifier, I got the internal picture on the internet which shows the IC's package i have attached the picture for your reference. https://obrazki.elektroda.pl/9977746600_1487384734.jpg
The missing IC4 circuit seems to be a MMIC amplifier.
The signal output of the IC3 (MAR04) it goes to C9, and from there to IC4 input.
IC4 is DC supplied through the L3 inductor (choke), and its output goes to C7.
From C7 the following circuit looks like a detector.
Anyway, seems that your analyzer needs that missing IC4 circuit, otherwise would be more useless components on the board.