MPP revE need help

[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]

Please post good pictures of:
- Solder side of your board
- new picture of component side - is the 3.3 Ohm resistor to coil really 3.3 Ohms - cant tell in the photo.
- how are the wires connected from pcb to coil - orange,grey,red,black,white - photo or drawing

in reference to this photo https://www.geotech1.com/forums/atta...8&d=1588671083

[Albdelafar]

If you have no signal from the secondary small coil it would seem that your detector is not transmitting a signal via its coil.

I agree with you but my signal change when a target is near the coil so I do not know what to believe.

The TX circuit is pretty straightforward. You've got the drive pulse to the gate of the MOSFET and then you've got your diode and coil and damping resistor.That's it. So not much to check by way of troubleshooting.So you can recheck everything, make sure the mur460 diode is good and correct orientation.Recheck the mosfet is good, etc.
Check the board connections are good.

I checked the board many times the components are in the right place I took a new picture . I checked conductivity of TX and RX pin to ground an i have no short. R10 is 3k3 ohm R7 is 10ohms. I noticed a 1M ohm resistance between the MUR460 in the otherside there are infinity resistance as expected.

Please post good pictures of:
- Solder side of your board
- new picture of component side - is the 3.3 Ohm resistor to coil really 3.3 Ohms - cant tell in the photo.
- how are the wires connected from pcb to coil - orange,grey,red,black,white - photo or drawing

in reference to this photo https://www.geotech1.com/forums/atta...8&d=1588671083

Hi you can see the solder side . The copper layer is a bit unstick on TX pin but i checked connectivity with R10 and R4 and it's good. No connectivity between TX and ground too.
For my coil connection TX and RX pins (midle pin of PL1 an PL2) are shorted on the coil plug and the other side of the coil is connected to ground on PL1 pin 1.

For the coil it is a 0.33mH 0.7ohm i added a serial 10 ohm resistor to up TC to 1/3 of the pulse width (100us).

[Qiaozhi]

Did you actually read the part in the Build Documents were it says:

"Please do not proceed to the next step until you have solved any problems encountered in the current step. If you get stuck at any stage during the build, then seek help in the Geotech forums before moving on. Do not simply populate the whole board; discover it doesn't work (which will be the most likely result) and then post in the forums: “I've built the Minipulse Plus, and it's not working. What's wrong?” …. as you will receive little sympathy from other Geotech members."

I ask this because it looks to me like you've populated the whole board.
Also, looking at the underside of the PCB, I can see several pads that appear to be shorted to the ground plane. It might be a good idea to tidy up the soldering.

[Albdelafar]

Did you actually read the part in the Build Documents were it says:

"Please do not proceed to the next step until you have solved any problems encountered in the current step. If you get stuck at any stage during the build, then seek help in the Geotech forums before moving on. Do not simply populate the whole board; discover it doesn't work (which will be the most likely result) and then post in the forums: “I've built the Minipulse Plus, and it's not working. What's wrong?” …. as you will receive little sympathy from other Geotech members."

I ask this because it looks to me like you've populated the whole board.
Also, looking at the underside of the PCB, I can see several pads that appear to be shorted to the ground plane. It might be a good idea to tidy up the soldering.

I read the document and I follow all the instructions. I just past the damping step because I was waiting for resistors and pot to do the damping resistor tool.
All the steps are working and the only problem I have is that I could measure the flyback voltage anywhere.
I know my soldering is not very good but I checked with multimeter the pads until the pre-amp stage and I get no shorts to the ground.
Another thing is when I change the damping resistor value the saturation time on TP3 change signe to me that my coil is right connected. And it is the same with my two coils.

[Polymer]

Albdelafar, in my components parts list R10 should be 3.3 Ohms NOT 3300 Ohms like you have! No wonder you are not getting much flyback.

Solder side, I agree with Qiaozhi - what solder are you using?

[Qiaozhi]

I read the document and I follow all the instructions. I just past the damping step because I was waiting for resistors and pot to do the damping resistor tool.
All the steps are working and the only problem I have is that I could measure the flyback voltage anywhere.
I know my soldering is not very good but I checked with multimeter the pads until the pre-amp stage and I get no shorts to the ground.
Another thing is when I change the damping resistor value the saturation time on TP3 change signe to me that my coil is right connected. And it is the same with my two coils.

I think you are making this far too complicated. Simply wind a coil with 22 turns on a 250mm diameter, and connect a fixed resistor of 680 ohms for the damping resistor. This will be suitable for testing. Adjust the main damping delay to 20us and connect a scope to the output of the preamp. Then take snapshots from the scope with and without a target, and post them here.
If you can also post a snapshot of the TX oscillator signal, that would be great.

[Qiaozhi]

Albdelafar, in my components parts list R10 should be 3.3 Ohms NOT 3300 Ohms like you have! No wonder you are not getting much flyback.

Solder side, I agree with Qiaozhi - what solder are you using?

Well spotted!
You can actually see the resistor is a 3k3 (instead of 3R3) from the photo of the board.

[surfdetector]

Well done Polymer

[Albdelafar]

Damn I really need glasses I readed K instead of R....
Thanks Polymer for this !! I think all be better with the good resistor value. I will try to replace it by 4 parrallel resistors 0.5w 3X 12R and 1X 20R to see if I can have a flyback voltage now.

For my solder it is a very simple 30w.

[dbanner]

Oh Lord, I waited so long to see that flyback pulse, please let me see it before I die from flybat virus.

Amen.

[Polymer]

Oh Lord, I waited so long to see that flyback pulse, please let me see it before I die from flybat virus.

Amen.

[Polymer]

Damn I really need glasses I readed K instead of R....
Thanks Polymer for this !! I think all be better with the good resistor value. I will try to replace it by 4 parrallel resistors 0.5w 3X 12R and 1X 20R to see if I can have a flyback voltage now.

For my solder it is a very simple 30w.

You are welcome! I mean what solder wire do you use. Leaded/Unleaded, brand name or chinese boat?

[Albdelafar]

Oh Lord, I waited so long to see that flyback pulse, please let me see it before I die from flybat virus.

Amen.

No more than me I have just finished the work, your relief is near !!

Polymer I use this one
Is a bit thick but they had not thinner wire at store.

[Albdelafar]

And TADA
Big thank you to all of you for your help and your time !! My bad for this stupid mistake.
Polymer elected as winner
If you comme in south of France I give you one of my own brewed beer or two !!

[surfdetector]

Glad to see a successful conclusion to this one