New to debugging. How to go about finding a mistake in this exponential voltage converter

Question

This is the exponential converter I'm trying to set up:

Marked in purple are the measurements I have taken. As far as I can figure out the first part is working correctly OpAmp is giving the expected output proportional top input voltage. The second part with (-0.74,-0.77,11.39) measurements don't seem to to change with input voltage. I have checked everything 10 times and not sure how to go about debugging this.
I 3x checked every resistor value and replaced every OpAmp and transistor just in case of damage.

Cristobol Polychronopolis · Answer

I'm not sure what your theory of operation is, but the base of Q2 is grounded. The common emitter junction won't go below -0.77V, because Q2 will supply plenty of current through its B-E junction. That means Q1 will remain off as long as the U1.1 output is negative, which it will be unless the inputs sum to less than -5V to overcome the effect of the 5V supply biasing U1.1. Clearly, as long as Q1 is off, U1.2 will be at roughly VEE, and there won't be any other signal propagating from input to output.

Answered by Cristobol Polychronopolis on December 29, 2021

New to debugging. How to go about finding a mistake in this exponential voltage converter

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