Tesoro 10" concentric repair question

[Stefano]

Hi,
I have a Tesoro 10" concentric coil which needed repairing. I opened the shell and made the rewiring of the cable to the coils. Hopefully I was able to recognize where each wire of the shielded cable was connected to, because a bit of plasting was still in place. Then I welded also the wires in the connector as in the origin and as it is shown in the picture I found here. So:

Grey pin 4, Purple pin 3, shield pin 5, Orange pin1,

Inside the coil shell I connected purple and screen together, then to the side of each coil (RX & TX) and to the wires that goes to the conductive paint surface for the screening. I think everything is correct, in fact if I measure on the connector I get:
23 ohm and 6.16mH between 3 & 4
24,5 ohm and 6.04mH between 5 & 1
0,2 ohm beetween 3&5 (cable screen resistance)
The coil is working, not extremely well, since it's not better than the 8" coil but works, the problem is that when I touch any metal parts of the MD (TEsoro Conquistador) like the switch or the connector for example, the threshold set in all metal mode decreases (disappears), while touching in Disc mode produces most of times a false signal.
I can't guess the reason. Notice that this happens even when the two half shells are closed one over the other!

Any tip?
Thanks
Stefano

[Qiaozhi]

Hi,
I have a Tesoro 10" concentric coil which needed repairing. I opened the shell and made the rewiring of the cable to the coils. Hopefully I was able to recognize where each wire of the shielded cable was connected to, because a bit of plasting was still in place. Then I welded also the wires in the connector as in the origin and as it is shown in the picture I found here. So:

Grey pin 4, Purple pin 3, shield pin 5, Orange pin1,

Inside the coil shell I connected purple and screen together, then to the side of each coil (RX & TX) and to the wires that goes to the conductive paint surface for the screening. I think everything is correct, in fact if I measure on the connector I get:
23 ohm and 6.16mH between 3 & 4
24,5 ohm and 6.04mH between 5 & 1
0,2 ohm beetween 3&5 (cable screen resistance)
The coil is working, not extremely well, since it's not better than the 8" coil but works, the problem is that when I touch any metal parts of the MD (TEsoro Conquistador) like the switch or the connector for example, the threshold set in all metal mode decreases (disappears), while touching in Disc mode produces most of times a false signal.
I can't guess the reason. Notice that this happens even when the two half shells are closed one over the other!

Any tip?
Thanks
Stefano

I have also noticed this before. In my case I was using a metal connector and a metal case, and was able to cure the problem by connecting the metal case to 0V.

[Northerntrowel]

I had the same problem too...

....On my homemade BandidoII .I resolved the problem like Qiaozhi said .
I use a Tesoro coil too!(8" brown donut).

JF

[Stefano]

I'll try and let you know. Anyway the strange is that I own 2 other coils, 1 concentric brown polo 8" and 1 DD Laser 8" and in none of them the connector body is connected to the cable shield.

Stefano

[Qiaozhi]

Interestingly I've just had the same problem with a Tesoro Laser coil. Eventually I traced it to an erratic cable connection at the connector. After resoldering the (eventually) broken wire back into position, there was no longer any signal generated when I touched the metal connector, and no need to connect it to 0V.

I also noticed that when I touched the Laser coil on the fancy label stuck to the top of the shell, there was a signal generated, but nowhere else. The label looked suspiciously like it was metallic ... so I pulled it off ... and guess what? It was metal foil!! How stupid is that?

[Stefano]

Thanks Quiaozhi for the info.
Unfortunately my coil has not stickers at all on it. Even the s/n label is not where it should be.
When I went back to my parent's house last day (where my shack and my MD stuff is) I checked about the 0V connection solution. It seemed to become better however it wasn't completely fixed. I also disconnected the spare wire (the blu one),which I originally connected to the pin#2 in the connector and left n.c. inside the coil shell, from the connector pin, so that now it's completely disconnected on both sides.
As I say: the situation seems now better, but I need more time to investigate this very strange behaviour.
In the meantime thanks to all for the help.

[Qiaozhi]

Thanks Quiaozhi for the info.
Unfortunately my coil has not stickers at all on it. Even the s/n label is not where it should be.
When I went back to my parent's house last day (where my shack and my MD stuff is) I checked about the 0V connection solution. It seemed to become better however it wasn't completely fixed. I also disconnected the spare wire (the blu one),which I originally connected to the pin#2 in the connector and left n.c. inside the coil shell, from the connector pin, so that now it's completely disconnected on both sides.
As I say: the situation seems now better, but I need more time to investigate this very strange behaviour.
In the meantime thanks to all for the help.

Yesterday I investigated this problem some more. It appears the dodgey wire connection was a red herring. Now I think I understand what's going on.
Firstly I plugged in the connector but without the metal covering on the plug. Then I moved the metal plug over the connector without allowing it to connect to the metal body of the socket. If I then touched the metal body of the plug, the noise injected by my finger was capacitively coupled into the input stage. There are two ways to fix this noise problem. Either connect the metal body of the connector to the screen inside the plug, or connect the metal case containing the detector electronics to 0V. Personally I made the connection in the plug, which also stopped any noise caused by touching any of the metal parts of the detector. Either solution will fix the problem.

[Stefano]

Sorry for latency but just last week-end I have been able to test my "fixed" coil on the beach (dry sand of course).
As I stated before I solded the coil connections inside the shell and connected the cable shield to the connector body. This seemed to reduce the instabilty, however it wasn't perfect as the 8" brown polo is.

Well, the test on the beach showed that the problem was not cured at all. The coil gives continuosly false signals and is extremly noisy, while the other one is working silently and well under the same conditions.
I have no idea what else I could check, except thinking that this coil, bought as "not working" on eBay, was really defective since the beginning and never worked ...

[Max]

Sorry for latency but just last week-end I have been able to test my "fixed" coil on the beach (dry sand of course).
As I stated before I solded the coil connections inside the shell and connected the cable shield to the connector body. This seemed to reduce the instabilty, however it wasn't perfect as the 8" brown polo is.

Well, the test on the beach showed that the problem was not cured at all. The coil gives continuosly false signals and is extremly noisy, while the other one is working silently and well under the same conditions.
I have no idea what else I could check, except thinking that this coil, bought as "not working" on eBay, was really defective since the beginning and never worked ...

Hi,
do you own an analog or digital scope ? If so you can test if coil is damaged that way:

- connect TX part of coil to TX connector leads on detector (oscillator)
- connect RX leads to a dummy load made that way : 15nF poly capacitor + 1Kohm resistor, all parallel I mean RX coil + cap + resistor
- connect the scope by a 1:1 probe to the parallel of above and read peak to peak value when coil is far away from metals (e.g. suspend with a nylon wire or something or use a wooden table)

Results:
- if you read from 1mV to 5mV peak-to-peak coil is perfectly aligned
- if you read from >5mV to max 30mV pp coil is still good and has just minor damages or few bad alignment
- if you read more than 30mVpp you'll be sure that coils have permanent damage inside cause of hit or something... so don't waste your time with it , you can't do anything good at that point : buy another or try make one yourself if you can

To make measure you need scope... don't try with multimeter cause you'll get wrong readings almost sure.

Kind regards,
Max

[Qiaozhi]

Sorry for latency but just last week-end I have been able to test my "fixed" coil on the beach (dry sand of course).
As I stated before I solded the coil connections inside the shell and connected the cable shield to the connector body. This seemed to reduce the instabilty, however it wasn't perfect as the 8" brown polo is.

Well, the test on the beach showed that the problem was not cured at all. The coil gives continuosly false signals and is extremly noisy, while the other one is working silently and well under the same conditions.
I have no idea what else I could check, except thinking that this coil, bought as "not working" on eBay, was really defective since the beginning and never worked ...

Quite often you will see Tesoro coils advertised on eBay as being physically in good condition, but with a note that it gives false signals when brushed against grass. I have never had the chance to test a coil with this problem, but I suspect that the electrostatic screening has failed in some way. You should be able to test this by monitoring the RX signal while you bring your hand close to the coil. If the shielding has failed, the capacitance introduced by your hand should cause a change in amplitude.

[Stefano]

Thanks for replying Qiaozhi.
Yes I own a 50Mhz dual ch. analog scope. I'll do the test you suggest, expecially the one for checking the efficiency of the shielding, because I had to replace the bare wire glued to the conductive painting on the bottom part of the shell. Since I don't have any kind of conductive painting, I just glued it again in three points with a "hot-glue gun" and then put on it, over the whole lenght, a strip of strong tape. The multimeter showed a good electrical connection, or at least similar to the one on the other shell ( I don't remember exactly but some kOhm between this wire and the multimeter probe point put on the black painting).
Then I'll let you know the result a.s.a.p. (ther's a new born just know at home, so I have very little free-time ).

[Stefano]

...forgot to thank you Max as well...
Sorry.

[Max]

...forgot to thank you Max as well...
Sorry.

Hi,
you can use graphite spray for shield wire repair... use a silvery looking ethernet-like (same as old telephone twisted pairs) wire and glue it down with hot melt glue in 2 or 3 spots as you described... then mask around with paper and lose masking tape leaving a strip around the wire where you need make the connection... then use graphite spray (also fishing pole stuff is ok, always graphite inside) e.g. Kontakt or similar brand.

Graphite will make a large layer extending from wire to the base and making a very good contact.

Best regards,
Max

[Stefano]

Yes I read about the conductive paint that most of you use to make your own coil, and I looked for it, but I have not been able to find it anywhere of any kind near where I live in Italy. The only option would be buying from a national supplier in Milan but it is too much expensive even for just 1 can!
In fact when I tried once in past to make a coil for a HH1 PI I used for screening the metallized film of a poliester capacitor, because I found no any other chance to make it.
Anyway, trying to find "Graphit 33 of CRC Industries - Kontakt-Chemie" (I think you suggested this one), gives no link in Italy...
Just wondering.... How much is the price for 1 can out there??

[Max]

Yes I read about the conductive paint that most of you use to make your own coil, and I looked for it, but I have not been able to find it anywhere of any kind near where I live in Italy. The only option would be buying from a national supplier in Milan but it is too much expensive even for just 1 can!
In fact when I tried once in past to make a coil for a HH1 PI I used for screening the metallized film of a poliester capacitor, because I found no any other chance to make it.
Anyway, trying to find "Graphit 33 of CRC Industries - Kontakt-Chemie" (I think you suggested this one), gives no link in Italy...
Just wondering.... How much is the price for 1 can out there??

Hi,
it's strange that you cannot find there... it's still used in electronics for shielding of e.g. RF works and microwaves expecially... but also for a number of other things...

In the EU (apart UK) the price is about under 10eur for a 200mL can , electronic grade.

You can try find a can of it used for other stuff... not electronics I mean (but it's about the same stuff in the can , graphite superfine graines + ether + propeller) ... you can look for ball bearings lubricant spray or much better fishing stores... cause hi-quality carbonium type fishing rods need often that treatment -> both are about the same stuff you can find in electronics grade cans.

Best regards,
Max