TF-900_TM800

[ivconic]

Carl, take pity and dig through your hidden treasure trove of detectors... you might find something like this that you didn't even know you had!
And then take a picture of what's inside!

[pito]

But!
The story is not over yet!
I have only two pictures of something pretty intriguing (at least for me).
It is "gold module" as I heard.
As I understand; it is addon for these detectors.
And that's about all I know, no more details!

nothing special, separate Tx with option (clip ) to use all frame as Tx antenna.

https://patents.google.com/patent/US4348639A/en

[pito]

I see you have your own and fisher TM800, you can compare transmitters of them just using similar coil as on picture connected to oscilloscope, holding it at the same distance from Tx antennas.
Then you will know how good is your transmitter.

[ivconic]

I sold Gemini II long time ago. Don't have any data on coils.
Sorry.

[Carl-NC]

It's not a gold module, it's a TX module for tracing buried pipes. You clip the TX module onto the exposed pipe and then use the TF900 to trace the signal. Similar to how the Gemini works. I don't have the module.

[ivconic]

That makes sense.
So, most probably one of the "merchants" renamed it "Gold Module"...
Now it is at least easy to guess what kind of circuit it is, probably similar (if not the same) TX as in the device.

[berreizeta]

Ivconic,

This discrepancy between the pcb and the schematic, have you been able to find out what is correct?

According to the scheme 6k8 goes to REF OUT but on the board it goes to VCC1 :

[Skippy]

The 6k8 resistor goes to VCC1, pin8 of the LM358 IC that's mysteriously labelled as U5 on the above CAD drawing, and shown as U4 on the original PCB.
LM393 opamps have weak pull-up ability on their output, this 6k8 provides additional pull up current, making it faster, which is what the digital inverter wants.

[ivconic]

Ivconic,

This discrepancy between the pcb and the schematic, have you been able to find out what is correct?

According to the scheme 6k8 goes to REF OUT but on the board it goes to VCC1 :

Yelllow is correct.
BTW it is not my PCB draw.

[berreizeta]

Ok, I make the change in the board design

On the RX coil board you indicate 13mH, do you know the measurements for the TX coil?

I assume it will also be 13mH (75turns), do you know the value for the 14 turns?

The inductance value of 13mH is only the toroid with the 75 turns, or the toroid with the loop included ?

[berreizeta]

I think U5 is correct:

[ivconic]

...The inductance value of 13mH is only the toroid with the 75 turns, or the toroid with the loop included ?...

Measured complete coil (windings on toroid) of course.

[pito]

My coils , 26t = 6.3mH, 75t = 20 mH, I will soon test Tx part of the circuit.

[Skippy]

Quote:"I think U5 is correct"
I didn't say there was anything wrong with it. What I said was " U5 on the CAD layout is actually U4 on the original PCB"
Take a look at the original circuit board, you will see that U4 is printed next to that 8 pin device. Someone has renamed the part identification number, probably others too.
https://www.geotech1.com/forums/foru...248#post313248

[Skippy]

"probably others" is correct. U1 has become U3, U2 has become U1, U5 has become U6.... you get the idea ... total confusion.