MPP REV-E Step 7, Signal on TP4 does not respond

[convola]

Everything is normal until step 7, but in step 7 the signal looks like this and does not react at all. TP4 how can I solve this problem?

[Qiaozhi]

Assuming that the preamp output at TP3 is correct, and the power supplies to U3 are OK, then check the sampling pulses at Q1 and Q3.
If everything seems to be alright then you may a fitted a wrong and faulty component in the sampling integrator.
Can you post a photo of the PCB?

[convola]

Signals for J113 JFETs and TL072

[convola]

jfet drain and gate signals

[convola]

I think my JFETs is fake. they are acting like a transistör.

[Qiaozhi]

It is very difficult to debug this remotely. There's obviously something wrong in the sampling integrator.
If your opamps are in sockets, then remove them and check the signal path again. You should be able to isolate the fault that way.

[Carl-NC]

It looks to me that you are sampling 125us after the TX pulse. Is that right?

[convola]

The problem was caused by fake j113. I installed bf245 instead of j133 and it started to respond, but this time the signal decreases instead of increasing. I will try to install 4066.