Tracker IV Tx circuit

[dbanner]

Something doesn't look right about this part of the circuit. anyone familiar with it? Shouldn't the Tx coil be in the transistor collector. The pinout of the transistor shown on the PCB suggests this is the case. however the schematic shows otherwise. This setup is rather strange.

[kt315]

first and main rule. never do not trust aliens' schematics. do your own. your mistakes will be just your.

[dbanner]

I just need to trace out the scheme of the Tx circuit. It seems a bit strange. Something is interesting about this design, although the depth is limited.

[dbanner]

first and main rule. never do not trust aliens' schematics. do your own. your mistakes will be just your.

I compared the scheme with the PCB and whoever traced it did a very good job, except for the Tx circuit, everything else is correct. But it is not complete. The second half of the disc/all met/tone switch is missing from the scheme but that is easy to draw in. And the low battery circuit is omitted, no big deal.

[kt315]

there are two version of BH4 - thru hole board and SMD board. do you sure know the sch is for? i am not.

[Skippy]

It appears to me that what is shown on the schematic as Base / 1 is the Collector; Collector / 3 is the Base; the Emitter to 68R looks correct. Transistor is shown correctly as npn type.

[Altra]

DBanner, I have a complete pcb if you need me to check anything, Agree with Skippy, the base and collector reversed

[Skippy]

There sure are some peculiar things about that schematic.
Bizarre capacitor values, for one. I wonder if someone measured them in-circuit ?

[Altra]

Here is a top and bottom of the pcb

[dbanner]

It appears to me that what is shown on the schematic as Base / 1 is the Collector; Collector / 3 is the Base; the Emitter to 68R looks correct. Transistor is shown correctly as npn type.

I agree.

I redraw the main circuit, here it is. I will complete it with the corrections.

I also observed many similar designs which achieved decent detection depth- Harbor freight 9 function metal detector, for example. There was also the tracker II in the old style box which is essentially the same circuit but which was said to perform much better in terms of depth. I just wonder what is kneecapping the Tracker IV, are there some "magic" simple mods to improve performance.

[dbanner]

DBanner, I have a complete pcb if you need me to check anything, Agree with Skippy, the base and collector reversed

The capacitor values in the filter stages bother me.

I'm redrawing the Tx circuit along with the phase comparators. I want to simulate this section just to see what it's doing. It looks strange, but except for the incorrect transistor orientation, the rest of the circuit checks out(matches what's on the PCB.

[dbanner]

Work in progress.pdf

[dbanner]

I'll probably do a single side PCB with some changes to original scheme. Maybe I can jack up the performance a bit. For me it is a joyous hobby to build at home.

[Carl-NC]

there are two version of BH4 - thru hole board and SMD board. do you sure know the sch is for? i am not.

The thru-hole and SMT schematics are absolutely identical. The one shown has SMT 1% resistor values.

Agree with Skippy, the base and collector reversed

Definitely.

Bizarre capacitor values, for one. I wonder if someone measured them in-circuit ?

Looks like it. Corrected/missing values are:

C4,C13	10n
C2,C27	120p
C3,C5,C6,C8,C12	220n
C7,C9	3.9n
C11,C16,C22	22n
C14	470n
C17	6.8n
C20,C21,C23,C19,C26	100n
C24	1u

Also, U3-pin6 connects to U3-pin2, not pin1.

There was also the tracker II in the old style box which is essentially the same circuit but which was said to perform much better in terms of depth. I just wonder what is kneecapping the Tracker IV, are there some "magic" simple mods to improve performance.

The Tracker 2 is identical to the Tracker 4 except that the speaker driver has a 2-transistor gain stage which might give it the perception of more sensitivity.

[Altra]

My pcb is no longer functional

see attached cap values - measured off pcb

Also J5 and J2 go to the analog meter

Add: Thanks Carl