I don't understand your schematic.

You've got these two boxes that just say,"Latch circuit for ...." What is in those? The top line that comes out of the right side of each of those boxes, what is it? Is the coil in the green box the relay coil for the switches that are also in green boxes? Since your system only appears to have positive voltages, what is the purpose of the circled LEDs that require the top wire to be negative in order to illuminate?

You say the output of the VCO goes to 0.735V. Where does that magic value come from? Why can't if go to 0.5V or 0.9V instead?

Seems, you could not fully understand the block diagram.
I'll get you the detailed schematic shortly.

 

I don't understand your schematic.

You've got these two boxes that just say,"Latch circuit for ...." What is in those? The top line that comes out of the right side of each of those boxes, what is it? Is the coil in the green box the relay coil for the switches that are also in green boxes? Since your system only appears to have positive voltages, what is the purpose of the circled LEDs that require the top wire to be negative in order to illuminate?

You say the output of the VCO goes to 0.735V. Where does that magic value come from? Why can't if go to 0.5V or 0.9V instead?

Hi

Here is the detailed schematic.

This circuit is meant to read the TYPE and the CUT-OFF VOLTAGE of any VCO connected to it. Type means PNP or NPN circuitry.

As mentioned earlier, as long as the input voltage to a PNP-VCO is below the cut-off voltage, the output is (Input Voltage - 0.6) approx. And when the input reaches the preset cut-off voltage the output falls to 0.735V.

On the other hand, as long as the input voltage to an NPN-VCO is below the cut-off voltage, the output is in between 0.5 - 0.7. And when the input reaches the preset cut-off voltage the output shoots to the cut-off value.

Please refer to the graphical illustration for more better understanding.

I hope the circuit is self explanatory. All the parts of the circuit are working as expected, except the MAGIC output of the op-amp.................which is the actual problem.