Vallon VMH3CS Mine Detector

[stefan-s]

Thanks eric,

I will try it tomorrow.

[Ferric Toes]

It may be the connector which is causing the problem. Remove the connector and just solder the two coax's together. Splitting the coax through a metal bodied connector will generate eddy currents in the connector body. That is why I prefer plastic bodied connectors. If the connector is coaxial then that is OK as there is no external magnetic field to interact with the metal.

Eric.

[stefan-s]

Yes, both are modded an both does have the same problem.

I just tested the cable out of the enclosure first with the 6mm coax coil cable the problem was the same.
After the first test i changed the 6mm coax coil cable with the standard spiral vallon coax cable and made a connection from the outer shield of my connector to the battery - pin. After this change it seems a little less nervous i can set the sens on max 8/9 now but 12 is still not possible it will go crazy again. I tested in all channels and banks.

So maybe the problem is in the cable?

really frustrating.....

Hi Stefan,

Thanks for for sharing the photos. Am I correct in saying you have 2 Vallons and both are modded and both exhibiting the same problem?

Have you tested with the internal coil cable section out of the enclosure?
eg not running under the PCB and if so, did it still have the problem?
Did you remove the coax cable pins from the internal black socket or just cut the cable and fit the new 3 pin end?

The coax seems quite large, diameter I'm wondering if this is causing an issue?

[Mdtoday]

Hi Stefan,

Thanks for for sharing the photos. Am I correct in saying you have 2 Vallons and both are modded and both exhibiting the same problem?

Have you tested with the internal coil cable section out of the enclosure?
eg not running under the PCB and if so, did it still have the problem?
Did you remove the coax cable pins from the internal black socket or just cut the cable and fit the new 3 pin end?

The coax seems quite large, diameter I'm wondering if this is causing an issue?

[stefan-s]

The coil with the 6mm coax:


The coil cabel connector and the conector from the electronics enclosure stick togeteher. As you can see the 6mm coax comes from the coil and the original Vallon coax is connected to the connector which is fitted in the enclosure.


Here you can see the original vallon coax who is comming from the connector in the enclosure and is fitted with the original connector on the board


This is how it is now (with the problems)

[Mdtoday]

Hi Stefan,

Can you post a photo showing your coil wiring and connections, it will help.

Brian

[Ferric Toes]

Eric,
Inside the electronics housing im using the standard coax cable.

For the coil im using this kind of coax:

What i have is a 3-pin connector, the inner wire is connected to one pin and the outer woven to the other. So one pin is not used. So what i will do is connect the woven shield also to the outer shell of the connector and from the outer shell of the connector i will connect it again to the battery ground?

Where or what is the TX/RX ground?

Sorry for the many questions but im new in this type of electronics. Maybe you can explain me in the easy way what to connect were.

Best regards
Stefan

Hi Stefan,

Here are the connections for the coil and also the battery connections on the underside of the sub board. This is the easiest to access and solder additional wires to. Do not connect the coax braid anywhere else. Use a piece of your cut off Vallon coax here. If you wish to ground the metal shell of the connector, run a wire to one of the battery - pins. I wouldn't even take it to the spare pin for safety.

Eric.

[stefan-s]

Eric,
Inside the electronics housing im using the standard coax cable.

For the coil im using this kind of coax:

What i have is a 3-pin connector, the inner wire is connected to one pin and the outer woven to the other. So one pin is not used. So what i will do is connect the woven shield also to the outer shell of the connector and from the outer shell of the connector i will connect it again to the battery ground?

Where or what is the TX/RX ground?

Sorry for the many questions but im new in this type of electronics. Maybe you can explain me in the easy way what to connect were.

Best regards
Stefan

[Ferric Toes]

Eric,

Much thanks for all the information, i really appreciate it

And what will i do with the woven shield of the coil cable connect it to one pin and to the outher shell of the connector?

Hi Stefan,
I am not clear on the type of cable you are using. Is it a coaxial cable with an extra shield i.e. a triax cable, or is it a shielded twin cable? For either of these you can connect the outer shield to the case/battery minus ground and also the outer shell of your connector. You must connect the ground side of the coil and any shield that you have on the coil, to the TX/RX ground. Make sure that the two grounds always remain separate.

A straightforward coax is all you really need and any extra shielding will not give any noticeable benefit.

Eric.

[stefan-s]

Eric,

Much thanks for all the information, i really appreciate it

And what will i do with the woven shield of the coil cable connect it to one pin and to the outher shell of the connector?

Hi Stefan,

With a test for resistance, the TX/RX ground is not the ground to the shielded box. However, the shielded box connects to battery minus. It appears that the TX /RX ground is connected to the box/battery negative via a capacitor, across which there must be a voltage, as the resistance measurment gradually increases up to around 100k. Therefore only use the existing TX/RX ground via the original coax connection for any coil modifications or additional coils that you make. You can ground the shell of your connector to the box/battery ground as Vallon do for the 6 pin connector.

The coax does not have to be the Vallon type as I have used RG58AU (or any thinner coax) on four coils now with no problems. If the total resistance is low, as it was on my 7in coil, then add a good quality metal film resistor in series to make it up to around 3.5 ohms. As I mentioned before, I put the resistor in the connector as they usually have metal end caps and if put in the coil you may get a eddy current response from these end caps. The Vallon will tune it out, but I prefer to start with a clean sheet.

Eric.

[Ferric Toes]

Hi Stefan,

With a test for resistance, the TX/RX ground is not the ground to the shielded box. However, the shielded box connects to battery minus. It appears that the TX /RX ground is connected to the box/battery negative via a capacitor, across which there must be a voltage, as the resistance measurment gradually increases up to around 100k. Therefore only use the existing TX/RX ground via the original coax connection for any coil modifications or additional coils that you make. You can ground the shell of your connector to the box/battery ground as Vallon do for the 6 pin connector.

The coax does not have to be the Vallon type as I have used RG58AU (or any thinner coax) on four coils now with no problems. If the total resistance is low, as it was on my 7in coil, then add a good quality metal film resistor in series to make it up to around 3.5 ohms. As I mentioned before, I put the resistor in the connector as they usually have metal end caps and if put in the coil you may get a eddy current response from these end caps. The Vallon will tune it out, but I prefer to start with a clean sheet.

Eric.

[Ferric Toes]

Hey Brian,

Before i had no problems.

The new cable shield is just connected to the pin. (its a one shielded cable so one cable inside and a woven on the outer side)

Sadly i cant use the original cable anymore because i cut it in pieces while i took the detector apart because i was thinking i dont need it again

Electronics housing is not connected to the 3 pin housing.

So i think i can conclude that i need to connect the coil cable shield to the connector outside and the connector outside again to the metal electronics housing? Or do i'm thinking wrong now?

For a test i will run the cable from the board to the coil connector on the outside of the detector instead of inside of the detector housing, its a easy test to see if it make any difference.

Stefan

Hi Stefan,

Your first comment is a valuable bit of information as it indicates that something isn't right with your modifications. However, do not try anything further with grounding before I check something. I may be wrong but I recall when doing some DC measurement when I first had a Vallon, that the coil ground is not the electronics case ground and that there was some voltage between them. Connecting the coil ground wrongly may cause a component failure which will be difficult to find and repair.
I will post as soon as possible, but hang fire till then.

Eric.

[stefan-s]

Hey Brian,

Before i had no problems.

The new cable shield is just connected to the pin. (its a one shielded cable so one cable inside and a woven on the outer side)

Sadly i cant use the original cable anymore because i cut it in pieces while i took the detector apart because i was thinking i dont need it again

Electronics housing is not connected to the 3 pin housing.

So i think i can conclude that i need to connect the coil cable shield to the connector outside and the connector outside again to the metal electronics housing? Or do i'm thinking wrong now?

For a test i will run the cable from the board to the coil connector on the outside of the detector instead of inside of the detector housing, its a easy test to see if it make any difference.

Stefan

Hi Stefan-S

Did you have problems before your mods?
Is the coil cable shield connected to the new 3 pin connector body or just to a pin?
Have you used original coil cable and just connected it to the new 3 pin plug?
Is the electronics housing connected to the 3 pin housing?
I am suspecting a shielding problem.
There is a switch mode type power supply on the connector PCB on the bottom side where I'm guessing you have run the coil cable.
I would try run the cable as far away from that area as possible.
Eric has successfully used a different coil connector so we know it can be done.

If possible, try and restore the original coil and cable assembly and connections to do a sanity check.

Brian

[Mdtoday]

Hi Stefan-S

Did you have problems before your mods?
Is the coil cable shield connected to the new 3 pin connector body or just to a pin?
Have you used original coil cable and just connected it to the new 3 pin plug?
Is the electronics housing connected to the 3 pin housing?
I am suspecting a shielding problem.
There is a switch mode type power supply on the connector PCB on the bottom side where I'm guessing you have run the coil cable.
I would try run the cable as far away from that area as possible.
Eric has successfully used a different coil connector so we know it can be done.

If possible, try and restore the original coil and cable assembly and connections to do a sanity check.

Brian

[stefan-s]

Hallo Erik, Carolina and Kingswood,

Thanks for all your help.

I tried all the channels and blocks with both my detectors and the problem doesn't ad all. ( in normal and minaral mode)
I have the same problems with both detectors one detector is with the original coil the other one with the 38cm coil.

There is only one thing that i changed on the detector, i made a connector for the coil in the front of the housing, the wire runs trough the detector housing not trough the stick as original should this give interference?

oh yes btw i know the glueing is a mess :P

of course i mean the problem is still there.