TGSL Tuning & troubleshooting

[simonbaker]

I just found one schematics that confirms your claim that EU, US and OTHER BF245 are not same pinout
I have not placed it by not looking at few pinouts myself ... and on PCB there is printed placement to right
it can be that it reversed or switched legs ...

don't know which is which ... where from silverdog bought these ...
marking for producer is FBG 62 or 82 BF245B
I am going to desolder them and try to see if they are blown and to try MD without them

Ok --TGSL won't work without JFets of course, but you can measure some DC voltages.

1. When measuring DC voltages, please also make an o-scope graph of same voltage so we can see if an AC signal is present (I know this is a lot of work, but hopefully we are getting closer). Especially LM393 pin 7 when LM358 is removed from socket.

2. Another possibility, which I doubt is the cause, is if somehow you got "P" type JFets instead of "N" type JFets, it might make those bad DC voltages you saw.

I'm not sure the best way to test your JFets -- maybe someone else can suggest. However, there should be a diode junction between the Gate and either the Source or Drain -- so maybe you can test that with a diode checker to see if correct type of JFet and if the pins make sense.

I just checked my J107 JFets with my multimeter diode checker.

With plus probe on Gate and neg probe on Drain or Source, I get approx .9V on diode checker. If I reverse probe polarity, no voltage (open circuit). If I check from Source to Drain, I get small voltage and beep (short circuit), either polarity.

Regards,

-SB

[sdesic]

Simon,

I don't know what would I do without your guidance...
Tested them out and seems that they are the same ... both good or ...
I am searching databases for producer of those FETs so I can determine their pinouts
most of them says that I have Gate on bottom (looking to right)
but I have found quite a few that say reversed from PCB ... China made ...
I am going to try reversing them and get back to you...

[simonbaker]

I just found one schematics that confirms your claim that EU, US and OTHER BF245 are not same pinout
I have not placed it by not looking at few pinouts myself ... and on PCB there is printed placement to right
it can be that it reversed or switched legs ...

don't know which is which ... where from silverdog bought these ...
marking for producer is FBG 62 or 82 BF245B
I am going to desolder them and try to see if they are blown and to try MD without them

I confirmed that BF245B (TO-92 style) leads are opposite to the J107 leads. Looking at Silver Dog PCB, I believe you must install the BF245B the opposite (rotate 180 deg) from what is indicated by the silkscreen outline. Perhaps that is your problem.

-SB

[simonbaker]

Simon,

I don't know what would I do without your guidance...
Tested them out and seems that they are the same ... both good or ...
I am searching databases for producer of those FETs so I can determine their pinouts
most of them says that I have Gate on bottom (looking to right)
but I have found quite a few that say reversed from PCB ... China made ...
I am going to try reversing them and get back to you...

Ok, maybe there are more than one pinout configuration. A diode test should confirm which is which. Hopefully they are still OK and not damaged.

-SB

P.S. I enjoy trying to solve mysteries, but don't always have the time I'd like to spend.

[sdesic]

EUREKA!
Detector works from first second.
Detecting more in depth.
Also has basic notch... I'll get back to you all with news.

Must say that on silkscreen it says BF245 not J107 ...

[sdesic]

Rotated those FETs... it is probably China made
Detector works with doubled depth.
No more delay 50s it detects instantly

1 Euro coin on 25 cm is quite good for unballanced and back from dead detector.
larger coin - army medal is found on 35 cm
disc mode works - aluminium foil and survival blanket are rejected on start
magnetic coin also is rejected by turning disc pot
ferrite is not yet rejected ... to be solved
in disc mode there is no noise...only on sens max

I must says that in all metal mode it is very much noise ...
I think sens pot is not working
when I touch components or disc pot it gives signal ...

[golfnut]

We can all breathe again well done

[simonbaker]

Rotated those FETs... it is probably China made
Detector works with doubled depth.
No more delay 50s it detects instantly

1 Euro coin on 25 cm is quite good for unballanced and back from dead detector.
larger coin - army medal is found on 35 cm
disc mode works - aluminium foil and survival blanket are rejected on start
magnetic coin also is rejected by turning disc pot
ferrite is not yet rejected ... to be solved
in disc mode there is no noise...only on sens max

I must says that in all metal mode it is very much noise ...
I think sens pot is not working
when I touch components or disc pot it gives signal ...

In workshop, usually lots of noise -- maybe too much for sens pot. But you can check with sensitive voltmeter if pot is changing threshold voltages at U106 pins 2 and 6. Also you can look at outputs of U105, U104 with scope (if it can show very low frequencies) to see your target signal and the noise level.

Also, did you change R29, R31, C14a,b and C17a,b to make less gain? That might help.

-SB

P.S. Perhaps we should have thought of those JFets sooner. Now we have good description of symptoms for next time. I think it would be good idea for Silverdog to have a different silkscreen outline for JFets when using the BF245B pin assignments -- very hard for kit builder to know to rotate the JFet opposite to outline.

[sdesic]

Yes, thank you all for your help.
This project would be trashed if there was no help from you guys.

Simon, Davor, porkluvr, golfnut you are greatest !

Must send my regards to Silverdog for this kit.
He must correct this error in silkscreen for us dummies who are building KITs

[sdesic]

Simon

I am now changing coil cable and replacing capacitors on to parts side od PCB.
No I have not done changes yet, I will test this again in quiet room or outside.
Will post that voltages as soon as possible.

[sdesic]

Changed all components to their proper side - and changed to USB cable
it is better ... little noise ... sens on 1/2 and it holds quiet

in ALL METAL mode
very low or none detection of silver coins like US quarter 1964 if they are flat to coil
if I place them verticaly the are found
aluminium coins same thing

other coins are found up to 30 cm

coils have moved from nulling position and I have 100-150mV on pin 7 353 ...
must correct that and then do ferrite notch thing...
I think with old cable it was better (for silver) or I moved coils from nulling position
must read PDFs again

[sdesic]

it is GB trimmer's fault ...
I really need to read documentation
sorry, silver is found again

[der_fisherman]

Yes, thank you all for your help.
This project would be trashed if there was no help from you guys.

Simon, Davor, porkluvr, golfnut you are greatest !

Must send my regards to Silverdog for this kit.
He must correct this error in silkscreen for us dummies who are building KITs

Actually its not a hard problem to fix, all Silverdog must do (I am sure he knows this already, he has been in this business for sometime now) is print a small piece of paper that shows the pin outs/orientation of all relevant parts. Print them off say 5 to a sheet of paper, cut them up and add one them to the kit. He can also post the same document here online as well......obviously any new PCBs will be marked differently to allow any of the correct parts to be correctly fitted.....its the same for ANY company, large or small, that supports its customers as good as possible, small mistakes will be made.
An old German saying says that "when you cut wood, you produce sawdust/chips".....
Regards
Andy

[sdesic]

Managed to null coils on 40mV pin 7 of LF353 U101a
managed to reject peace of ferrite (ring about 2.8cm in diameter or two of those together)
my GB trimmer is at 62.2k
but I reject US silver quarter but not smaller 1cm silver
it can detect quarter if I turn it 90 deg. if it is flat no detection
same with 30g silver round ... detects it if I "point it" to coil
I also lost aluminium coins 2,2 cm or it breaks sound - same rotation helps
smaller aluminium 1,7 cm it detects

same thing in all metal mode and in disc

when I turn GB pot to middle it comes back (big silver and aluminium)
I loose small silver 1 cm and small aluminium 1.7 cm

If I turn back GB trimmer to 40k it detects all and ferrite in all metal mode
ferrite and iron is not detected on disc

[simonbaker]

Managed to null coils on 40mV pin 7 of LF353 U101a
managed to reject peace of ferrite (ring about 2.8cm in diameter or two of those together)
my GB trimmer is at 62.2k
but I reject US silver quarter but not smaller 1cm silver
it can detect quarter if I turn it 90 deg. if it is flat no detection
same with 30g silver round ... detects it if I "point it" to coil
I also lost aluminium coins 2,2 cm or it breaks sound - same rotation helps
smaller aluminium 1,7 cm it detects

same thing in all metal mode and in disc

when I turn GB pot to middle it comes back (big silver and aluminium)
I loose small silver 1 cm and small aluminium 1.7 cm

If I turn back GB trimmer to 40k it detects all and ferrite in all metal mode
ferrite and iron is not detected on disc

Final tuning can take many experiments -- especially since all of us make different coils. Most people make several coils for that reason, and Ivconic found many times one coil is a dud and another works great without any obvious reason. He also does fine tuning of GB control "by ear" to not lose depth of coins -- with some possible ground sensitivity.

Things to check:

1. Coil polarity -- are RX leads reversed or not. When RX leads reversed, usually get a double-beep for targets at about 12 to 15 cm depth.

2. RX capacitor -- I don't know if you replaced .015 uF C6 with something else -- but small variations of capacitor can make a difference.

3. Coil shielding -- some people have different ideas and materials, you will see on this website.

4. Cable to coil -- you should be OK with USB as others have succeeded there, but other types can be tried.

5. Grounding of coil -- some people ground RX inverting lead to coil shield, some don't. Worth experimenting with.

Surprising that you detect coin "edgewise" but not flat -- were you using discrimination? What do you hold the coin with?

I think real silver may not be possible to discriminate out completely with the TGSL design -- may be perfectly normal.

I'll be gone for week, have fun! Good work getting your kit running.

-SB