MPP revE need help

[Albdelafar]

I know that. If I probe everywhere it's because nothing happen on tx on R4 and on the coil.. I tried on my two scopes with diferent probes on different point and i get no flyback voltage signal.

[dbanner]

Common (0V) is battery +.

With respect to probing the flyback voltage, would it not be in reference to -Vb or battery negative?

[Albdelafar]

And the winner is sample delay !! I uped sample delay from 10 to 18us and now all it's right !!!!
The anoying point is that I think 18us saturation is high for a 0.33mH coil.
I added a 10ohm resistor to up the resistance to 11.6ohm with coaxial cable. Now my Time Constant is near 33us 3 times less than Tx pulse width.


Last thing is to find the good damping resistor but this step get me crazy. I did not see any flyback voltage anything .... I received my 100X probe yersteday I probed on Tx Rx and ground pin and nothing.... on the damping resistor connection nothing on the coil wire insulation nothing.
My probe is working properly I calibrated it with oscope signal.
I will try to measure SRF to find Damping resistor value by calculation.
Have you ever see that ?
Thanks
PS: I will replace R35 from 4k7ohm to 2k4ohm to get a minimum sample delay of 10usec
Alban

[Albdelafar]

Your image does not look like the correct signal from TP4 or pin 7 of the TL072CP ( which are the same)

This is what it should look like:

https://youtu.be/SfAfVpSj3-U

Are you certain that you are on the correct test point? I have made that mistake myself.

I got the expected signal when I soldered this board. I do not undersrtand why is not working now because I did modifications on connection pins on damping resistor and coil but nothing helse.
I take measures on TP4 and U3 pin7 to check my connection between them.
I have a signal on U3a exit (pin1) on U3b entry (pin6) but nothing happen on U3b exit (pin7) just a litle signal looking like RX preamp signal a lot atenuated.
I wonder too if my problem could comme from my sample delay who is set up to 10us when my coil puting more than 20us to go out saturation so 10us on the 17us of sample pulse width are during saturation of rx preamp. I will try to up my sample pulse delay after work.

[surfdetector]

-Signal exit at U3b is the same as TP4 [ATTACH]50148[/ATTACH]

Your image does not look like the correct signal from TP4 or pin 7 of the TL072CP ( which are the same)

This is what it should look like:

https://youtu.be/SfAfVpSj3-U

Are you certain that you are on the correct test point? I have made that mistake myself.

[Albdelafar]

When probing TP4, try changing the time base on your scope when probing TP4. Just a hunch, but I think maybe the integration is working fine.

Why do you think time base could be the threat ?
In post #59 I checked diferent integrator pins with 400us T/div and as you could see there was a drop voltage when target was close to the coil on pin 1,2 and 6 but nothing on TP4.
I will do the test after work. Thank you for the advice.

[dbanner]

TP4 DC increase with Target passing near to coil.Later in the video.https://www.youtube.com/watch?v=OyS8sfv0XJ0&t=302s

[dbanner]

When probing TP4, try changing the time base on your scope when probing TP4. Just a hunch, but I think maybe the integration is working fine.

[Albdelafar]

I did it and signal decrease as expected more than pin 2 and pin 6.

[surfdetector]

Try probing pin 1 of the TL072CP do you see any change when you put a cola can near the coil?

[Albdelafar]

Ok so I did some tests and I still did not find the problem. All my pin connections was great and replacing my TL072CP by a new TCE2072 did not change anything.
So I checked my JFETs with scope but I do not know what is expected.
I took some screen shot if you want take a look on it
Thanks.


I see a difference between Q1 and Q3 on S pin :
On Q1 signal go down when a target is near the coil nothing happen on Q3 I think is because Q1 is for sampling and Q3 for EFE but i'm not sure.

[dbanner]

If replacing the chip solves the problem, then you have to ponder what happened to the other chip!

[Albdelafar]

I think JFETs are in the right way because when I soldered components at this step a target increased voltage on TP4.
I took a look and the position of JFETs correspond to the PCB solder mask.
I will try with a TL2072 after work.

[Polymer]

Hello,
So this step is good with the shunt between TX and R1 I think the tx pad was damaged when I changed the pin. What ever now my TP3 signal is good noisy but looks like normal !!
[ATTACH]50139[/ATTACH]
Next I adjusted R37 to have a minimum sample delay of 10us as you can see on TP6.
[ATTACH]50133[/ATTACH]
On the next step something differ from what is expected.
-EFE delay pulse width is expected to be approximately 100us but it is 118us as you can see here.[ATTACH]50135[/ATTACH]. I'm no worry about it but it is close to 20% difeerence.
-Pulse width at both TP9 (sample pulse width) and TP10 (EFE pulse width) is expected to be approximately 10us but I measure 17.6us that i think is more anoying because it's 76% more than expected....
[ATTACH]50136[/ATTACH][ATTACH]50137[/ATTACH]

Do you think my CMOS could be the problem ? I bought CD14538BE instead of MC14538BCP who was not available. I used 1% resistors and 5% polypropylene capacitors (oversized 2.2 nF_330 V ; 10 nF_630 V) and a 10% ceramic capacitor for C13 (220 pF_500V).
I join a picture of my PCB with components [ATTACH]50138[/ATTACH]

I would say your values are in a range that works well (among many).
I have pulse width 31us
TP8=111us
Sample width 17us.

Did not read everything here, but you may want to see if your jfets are inserted the wrong way around. This happened to me, datasheet misread.

[Albdelafar]

All precedent step was good. Only my pulse timings differ a bit from what is expected but like I saw on your video this is not a critical point.
My signal drop with a target before and after my first sampling integrator TL072CP pin2 and pin6 (U3a) but nothing after the second on pin7 (U3b).