the red squar block.I don't know completely what is its pupose.the blue one I know we can switch each single transistor at a time to make pulses and ,every single transistor has a different resistor attached with its collector. to limit current I guess. I don't know why they use different current levels.
finaly the green squar its too complicated.
best regards.
General strategy for simplifying and reversing a schematic. Redraw it as follows:
try to eliminate anything on the schematic which is there for protection or not directly involved in the measurement..like clamp diodes, display circuitry, bypass caps, voltage regulator support circuitry etc..
replace any voltage source like "battery" or voltage regulators with a fixed voltage that is either what you know it is or what is typical
if there are switches pick a position and analyze the circuit in that configuration
if you know of any driving waveforms then draw them on the schematic. For instance if you know "P24" is always a 100KHz square wave then draw it.
re-layout the subcircuits in a way that is easier to read.
get rid of any refdes, part numbers, or values which are not that important and do not help you understand the circuit..for instance 1N4148, etc..
The idea here is to take as much load off your brain as possible so it can try to analyze only the important part of the circuit. Schematics aren't always drawn well. Something very simple could be totally obvious drawn one way, and totally obscured drawn another. And this can vary from person to person.