MPP revE need help

[surfdetector]

Alban , connect to TP3 with your oscilloscope and put the cola can near your coil. Do you get a voltage drop there?

[Albdelafar]

Thank dbanner for the advice. The anoying thing is that when I soldered components this step was good .....
I will check the pin of the chip tomorrow it's late here. I use J113 bought on aliexpress.
I have only a TL2072 it is supposed to be a good replacement for Tl072.

[dbanner]

I think the DC level is supposed to increase (TP4) when the cola can is placed near to the coil.

It looks as though nothing is happening. Make sure the chip is inserted correctly.

Check for continuity between the socket and the board for each pin of the chip to make sure it's soldered in properly.

Replace the chip.

I assume you used J113's for the fets.

[Albdelafar]

Your attachments are not working. Please check them. Thanks.

They was working when I post my message i'ts strange and I can't edit my message ...

-Signal entry (CH1) at U3a without target and with target
-Signal entry (CH1) at U3b without target and with target
-Signal exit at U3b is the same as TP4

[surfdetector]

Thanks surf detector so my problem is not comming from that....the differences probably comme from components and pcb resistance.
I'm still learning.
In the next step at TP4 the signal do not move with a cola can whatever the coil I use....
So I tryed different measurement of the signal on the sampling integrator :
-Signal entry (CH1) at U3a without target [ATTACH]50140[/ATTACH] and with target [ATTACH]50141[/ATTACH]
-Signal entry (CH1) at U3b without target [ATTACH]50142[/ATTACH] and with target [ATTACH]50143[/ATTACH]
-Signal exit at U3b is the same as TP4


I suspect my TL072CP to be broken.

Your attachments are not working. Please check them. Thanks.

[Albdelafar]

Thanks surf detector so my problem is not comming from that....the differences probably comme from components and pcb resistance.
I'm still learning.
In the next step at TP4 the signal do not move with a cola can whatever the coil I use....
So I tryed different measurement of the signal on the sampling integrator :
-Signal entry (CH1) at U3a without target and with target
-Signal entry (CH1) at U3b without target and with target
-Signal exit at U3b is the same as TP4


I suspect my TL072CP to be broken.

[surfdetector]

Test Point 9 and 10 are here:

https://youtu.be/2VfvT_yaNBQ

[Albdelafar]

I saw them.
Your EFE pulse width is close to mine 114us vs 118us but you don't show your pulse width at tp9 an tp10.
I don't know if I can consider this values as normal.

[surfdetector]

Hi
If you look at these two short videos you can compare my build at this point with your results:

https://youtu.be/24h2qlO2ggg

https://youtu.be/l3dw_DcMhgw

My readings do not line up exactly with the build document but seem to be fine and consistent.

[Albdelafar]

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 !!

Next I adjusted R37 to have a minimum sample delay of 10us as you can see on TP6.

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.. 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....


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

[Albdelafar]

Hi surfdetector I tryed to measure signal to R1 and that was a good idea because i had no signal.....
Only noise I think because i measured a very litle signal who was the same with or without the coil pluged in. So I checked again my two coil and all seems right so I thought to measure the resistance between RX pin and R1 and bingo it was infini. I probably broke something when i changed all the connection pins .
I will try to correct that tomorrow and I hope that will resolve my problem.
@dbanner thanks i will try with scotch. JLPCB sent me for free with my purchase of felezjoo PCB.
Thank you for helping and sorry if my english is not verry good I do my best.
Alban

[dbanner]

It is good to put a small heatsink on the mosfet. I have read elsewhere Scotch tape being used for isolation. Dependent on the pulse width, the transistor shouldn't dissipate much heat. Provided all else is within the recommendation of the build document.

[surfdetector]

But when i try to read signal at TP3 i see no differences with or whithout my coil plugged in. Do you think my NE5532 can be the problem ?
Thanks

Try probing before the NE5532 at R1 and then also at R8 what do your waves forms look like?

[Albdelafar]

Thanks you dbanner for the information i learned something. Do an isolant tape can do the job if the IRF840 don't heat to much or a mica foil is necessary ?
For my problem i did a new measurement and i found my tx signal at my coil plug is good as you can see :
CH1 is at TP2 after NE555 and CH2 is on my coil plug after my coaxcial cable.

But when i try to read signal at TP3 i see no differences with or whithout my coil plugged in. Do you think my NE5532 can be the problem ?
Thanks

[dbanner]

Any transistor with a metal tab should be isolated from the heatsink.
You can use mica wafer(insulating pad) and appropriate nut and bolt with sleeve. Heatsink compound is used in conjunction.

If you are grounding your box for shielding, then if the mosfet isn't electrically isolated from the heatsink and accidentally touch the box. Well you can see the results.