I have built the circuit shown below.
The problem is that the circuit only works when I connect oscilloscope probes between node-A and the ground.
If I remove or decouple the probe-ground from the circuit ground then circuit does not work. I have ensured that all grounds are intact.
IC U5 is a TL082 op-amp being used as a differential amplifier. U6 is LM393 op-amp comparator circuit being used as a zero crossing detector.
Do I need to use a decoupling capacitor? I think I do not need a decoupling capacitor because the circuit starts working as it should the moment I connect the probe-ground wire to the circuit ground.
Any clue what mistake I am making?
After the first 5 comments, I am updating the circuit as follows. The components in red show my understanding after comments.