TM800

[Geo]

Geo, here is an excerpt from the TM600 manual. Based on what I see in the TM800 schematic (supposed to be identical to TF900). Cave mode may just be manipulation of null setting.
The TM600 can find voids according to docs by adjustment in the null setting. The null controls we removed from user control on later models and made trim pots to be set at factory.

I know all them.... but i am looking for the way that discovery makes the frequency change at TF900.
I want to construct a 2Box for caves at bigger depth by using large coils at bigger distance etc.... so i am looking for some details..

Btw.... thanks for the schematic

[Koala]

but i am looking for the way that discovery makes the frequency change at TF900.

Don't think http://www.chinametaldetectors.com/M...al%20detector/ Will be the same detector. After all they have been selling copies of high end MinLab detectors and Discovery are no longer in business. Could not find any two frequency TF900 pre 2011

[Ism]

Glad to be able to contribute to the family in a tangible way.

[Geo]

Don't think http://www.chinametaldetectors.com/M...al%20detector/ Will be the same detector. After all they have been selling copies of high end MinLab detectors and Discovery are no longer in business. Could not find any two frequency TF900 pre 2011

If i"ll finish my project i"ll try the second frequency (73.5 Khz). Maybe the China people to found something usefull....

[Ism]

My TM600 (almost identical to TM800) has a couple things that I would like to verify.
It has several zero ohm resistor. Why used instead of jumpers?
It has a capacitor labeled 1uf/10/100. Is that 1uf/10%/100v?
Last, it has drift when tying to set the null. The threshold goes from quiet to loud. Doesn't matter how long it is on or how many times I adjust it.
The original owner left batteries to rot in it and there is now a film on the PC board that I washed but the film is still there.
Ultimately I would like to make a new board, but for now, are there any recommendations? Parts replacement for 40 yr. old components?
I replaced all electrolytic caps and pots so far. I haven't tested it since I changed caps.
Thanks, Ran

[Koala]

My TM600 (almost identical to TM800) has a couple things that I would like to verify.
It has several zero ohm resistor. Why used instead of jumpers?
It has a capacitor labeled 1uf/10/100. Is that 1uf/10%/100v?
Last, it has drift when tying to set the null. The threshold goes from quiet to loud. Doesn't matter how long it is on or how many times I adjust it.
The original owner left batteries to rot in it and there is now a film on the PC board that I washed but the film is still there.
Ultimately I would like to make a new board, but for now, are there any recommendations? Parts replacement for 40 yr. old components?
I replaced all electrolytic caps and pots so far. I haven't tested it since I changed caps.
Thanks, Ran

It has a capacitor labeled 1uf/10/100. Is that 1uf/10%/100v?

sounds right to me

It has several zero ohm resistor. Why used instead of jumpers?

seen single sided board the use 0 ohm resistors as jumper before

As for the drift I wounder if damp has got inside one of the potentiometers

[Koala]

Noticed the TM800 only has half the component count of the TM808

Is the extra complexity of the 808 worth the cost and effort

[kt315]

I want to construct a 2Box for caves at bigger depth by using large coils at bigger distance

still one dreaming? cave mode is same like as disc mode in 5900 6000 di pro. one diagram. disc mode has low depth vs all metal mode.
it is rule and big problem of similar schemotecniks. you will not get good result. leave it and look something from magni.

[Geo]

It is not exactly the same. At TM800 don't use the phase shift to detect the caves. It uses a peak detector (see Q6, D3). This is the reason that TM800 is more sensitive than the TM808. Also if the distance between coils is bigger, i can give more power to Tx coil.

Regards

[Ism]

It has a capacitor labeled 1uf/10/100. Is that 1uf/10%/100v?

sounds right to me

It has several zero ohm resistor. Why used instead of jumpers?

seen single sided board the use 0 ohm resistors as jumper before

As for the drift I wounder if damp has got inside one of the potentiometers

Koala, The pic is of the board before I installed new pots and electrolytic caps.
I also installed header connectors (polarized plugs) for the coils/switch/meter/wires, and socketed the chips.
I checked the many waveforms and they appear to be as the schematic indicates, but still a drift in threshold intensity.
Thanks for you help.
Ran

[sarcheshmeh]

www.facebook.com/groups/207236096151354

[Jose]

Hello everyone
Anyone know where to find a PCB for TM800.
thanks
Jose

[kt315]

is PCB you meaning bare blank, without components? if you want I can ask veltex his price. not TM800, but TM-808 board.

[Jose]

Thanks KT315
I meant a PCB that can be done at home.
Apparently TM800 scheme is not as complex so I think an interesting project to build at home.
Regards
Jose

[Ism]

Thanks KT315
I meant a PCB that can be done at home.
Apparently TM800 scheme is not as complex so I think an interesting project to build at home.
Regards
Jose

I put the posted schematic into DipTrace free version. So it took two boards double sided because of DT freeware limits. If you want my files, you can PM me your email and I will send m schematic and PCB files.
If you get DipTrace, you can verify my work and print PCB trace for making your own boards. You should be able to merge them for etchng PCB.
BTW, I only did the main board, not the antenna circuit boards because I am upgrading my TM600. I don't plan to go that deep into tearing it apart.