MPP revE need help

[surfdetector]

Clip your channel 1 probe around the insulation of the wire that is going to PL1 pin 2 and show what the signal looks like there.

[Albdelafar]

I tried too after reading a reply from waltr on an other thread but still nothing this way...

[dbanner]

There has got to be a flyback voltage, otherwise there are little green men walking around on the PCB.

[dbanner]

Oh, I forgot the revE is with mur460 diode.Try the probe on the mur460 cathode and mosfet.Maybe your scope will not be able to to see this point.Surely the analog scopes with 100x probe can do this job.

[Albdelafar]

IRF840 pins scope measurement here :

I took several videos on R10 with analog and digital scopes on MUR460 too.
https://drive.google.com/file/d/1dad...ew?usp=sharing
https://drive.google.com/file/d/1Lcv...ew?usp=sharing
https://drive.google.com/file/d/1Soa...ew?usp=sharing
https://drive.google.com/file/d/1abc...ew?usp=sharing

The only flyback voltage I can see is a more or less 400mv peak.......

[waltr]

The scope pic of IRF840 Drain looks like the Coil is NOT connected.
If coil is not connected or has an open or is connected to wrong place then there will be no flyback.

Carefully recheck coil connections.

[Albdelafar]

Hello waltr I checked many times my coil connections and it's like on the manual schematic and my TP3 signal looks like what is expected. So my IRF could be broken if I did not have signal like expected ? How the signal is supposed to be ?

I was thinking to another point this night did my problem can come from a bad coil wire insulation who not support the flyback voltage peak ?

[waltr]

Possibly the coil is shorted. That would give the TX pulse shape at TP3 but NO fly-back at the MOSFET Drain.

Still think the coil is open and what you see is completely due to the damping resistor, R4.

The TX pulse and flyback can be checked without a connection to the pre-amp.

Another way to test the coil is wind a small diameter coil, 2cm, of about 10 turns. Connect a scope probe to this small coil, both probe and its ground. Then place this small coil very near the TX coil, inside the TX coil's field.
If the TX coil is being energized and discharged then the small coil will see the changing coil current since this is a transformer.

[dbanner]

You probably have a degraded coil, not quite shorted, but there is leakage between the windings. Try another coil.
Otherwise how could you possibly have a DC response at tp4 with an open coil? Not possible.

[Albdelafar]

This coil work because I see voltage variation with a target near the coil.
I made 2 coils the first classic mono coil and the other a coplanar coil the coils was tested with my new composant testor as you can see on post #80 I get a 0.33/0.34mH for 0.7/0.8ohm coil resistance. I made them with the same 1mm coper enameled wire.
Today I took multistrand wire from electric wire i will try to do a coil with it.

[Albdelafar]

The TX pulse and flyback can be checked without a connection to the pre-amp.

I disconected R1 on this tests so pre-amp was not connected.

Another way to test the coil is wind a small diameter coil, 2cm, of about 10 turns. Connect a scope probe to this small coil, both probe and its ground. Then place this small coil very near the TX coil, inside the TX coil's field.
If the TX coil is being energized and discharged then the small coil will see the changing coil current since this is a transformer.

I will try this. Do the coil need to be close or open ?
Thanks

[surfdetector]

you need to connect your large coil to the metal detector and then the small coil leads are connected to the oscilloscope probe and ground clip. You put the small coil near the large coil and turn your detector on. If your large coil is working then you will see on the oscilloscope the induced signal from the small coil.

[Albdelafar]

I did some tests :
With the coplanar coil :
https://drive.google.com/file/d/1k2r...ew?usp=sharing

With a multistrand electric wire 0.200mh 0.7ohm nothing :
With a litle coil under the tx coil there is nothing too(probe connected to a side and ground of the probe on the other side).
I get this on the damping resistor tool when no coil is connected.

[surfdetector]

I did some tests :

With a litle coil under the tx coil there is nothing too(probe connected to a side and ground of the probe on the other side).

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

[dbanner]

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.