Trimmer potentiometer in Tracker IV

[jgedde]

Recently I took my 5 year old Tracker IV apart to replace the headphone jack. As an electrical engineer, I couldn't help studying the PC board inside. On the board there is a single adjustment. Out of curiosity, and also because I noticed the adjustment was at the fully counter-clockwise position (odd), I decided to play with the adjustment. It's not obvious what it does, but adjusting it to near mid-span seemed to allow the detector to detect deeper targets. For example, the detector with the stock 8" coil had trouble with a silver dime beyond about 3-4" or so. Now, it reliably detects a silver dime to 5-6". It goes into "monkey chatter" slightly easier than before, though. Perhaps this is because overall sensitivity is increased. I had never been happy with the unit and never found anything but trash, but the fun/usability factor is greatly increased now.

I am NOT suggesting you all run out and tweak your Trackers. I adjusted mine because:
1) I'm incurably curious (read as impetuous)
2) The unit is used as a "guest use detector" (not my primary unit)
3) I was unhappy with the detector to begin with and figured I couldn't make it worse.
4) I marked the pot position before I started.

If you decide to try this, do so at your own risk!

The reason for my post is to ask if anyone knows what this pot is supposed to adjust? A schematic would be ideal, but I'm sure BH doesn't publish it willy-nilly to protect their intellectual property rights.

John

 

[Ed in SoDak]

I've had a Tracker IV apart, but it's been awhile. Since it didn't belong to me, I didn't mess around inside. Did you take a pic while you had it opened?

Just guessing, but since it already has a "sensitivity" and "disc" control on the front panel, and the primary thing in detectors that might have some built-in variability is the coil, I'd think the lone internal control would have something to do with balancing the coil, setting the disc point or ground balance. On the Tracker IV, it might also set the meter sensitivity.

And yes, a fully shut-off variable does make one wonder why they needed a control in the first place. Was it ever "peaked" at the factory, or perhaps this unit was at the extreme end of the adjustment range. If the person who set it at the factory hit the limit of the control and hadn't found or barely hit a peak, I tend to think something else was out of spec. Either way, it sort of raises an eyebrow.

I'd want to check several units to see if there are any differences. Why put in a control if a fixed resistor or jumper wire would do the same thing electrically?

-Ed

 

[jgedde]

Thanks for the reply Ed. Unfortunately I did not take any photos. It would be difficult to do so since the coil jack's wiring didn't offer much in the line of a service loop thus preventing the PC card from being easily removed from the enclosure enough to see all of it.

My guess is that it is not "tune to peak" adjustment as these are typically not a resistance (but not always) but usually an inductor or a capacitor as found in radio or other circuitry with sharp tuning requirements (high-Q). I believe it is a gain or voltage adjustment of some sort. Nonetheless, the adjustment did make a noticeable difference in performance. No apparent change was made to the meter's operation - not that it is especially useful anyway.

As you pointed out, I too would like to be able to peek inside several units to see how they are adjusted. What I'd really love to know is the purpose of the pot - in other words: what does it adjust? You're spot on with your comments about the fixed resistor or jumper.

I thought it might affect the coil in some way: TX power, frequency, etc. I coupled an oscilloscope to the coil and saw no change in amplitude or frequency as the pot was adjusted. BTW: the Tracker IV's frequency measures 6.38 kHz.

Do we have any BH techs or engineers in the forum? Perhaps they could shed some light without revealing anything proprietary to BH.

Whatever the pot does, it's certainly a change for the better and restored my interest in the BH. Last night I cut a section out of the shaft to shorten it, in such a way that it can be reinstalled. That way my daughter can play with it. We had some fun recovering pocket change I "lost" in the grass (no digging). Good practice for her pinpointing and she gets keep whatever she finds!

Cheers,
John

 

[Cherokeefan68]

I picked up a used Pioneer 101 at an auction a few weeks ago, I had it apart to clean it up and I believe the circuit board came almost completely out of the case. I would be willing to take a few pics if you guys want them.. When I put batteries in the first time before I opened it up the detector was really prone to chatter. After I cleaned some debris out of the case, it works great. Not bad for $22.00 I think.

 

[Ed in SoDak]

The coil connector is a three-piece affair. Two outer halves have one screw each, they form a shell that holds the jack in place. Remove the screws, pop the assembly out a ways so the outer halves can be separated, then the center portion with the wires can be withdrawn from the front. To reassemble, insert a stiff wire into a pin to help guide the connector out the hole. Don't overtighten the screws, they will split the shell's screw collar and all is lost for keeping it snug.

I wish I hadn't sold my o'scope, but all I could manage to do was display waveforms from music. Interesting, but not that useful. Voltage regulator sounds as good as any adjustment. Think in terms of something the manufacturer didn't want the average owner messing with, but still something that typically needs setting to some optimal point. Just like with cars, it might be Friday's machines are not adjusted as well as Wednesday's.

My Time Ranger has three internal adjustments. I haven't worked up the courage to diddle with them. Besides marking the physical location, you can also take a direct reading of the control's resistance, capacitance or inductance. That way, you can return them to a more precise point of their original setting if you decide to reverse your twiddling.

-Ed

 

[GoGoGopher]

I have had my Land Star apart numerous times, and there are 3 potentiometers on the board...I would recon they are for DISC, SENS, and Ground Balance fine tuning...
I would think yours is for Ground Balance adjustment...


HH,

 

[jgedde]

You may well be right. That would also explain the inceased sensitivity I get in my case. The ground around here is rather low in mineralization and I can usually run my detectors at near full sensitivity (I often can run at full sensitivity with my Spectra).

I recently pulled up a Levi's jeans rivet at 9-10" with the Spectra - try that with highly mineralized ground... That's not meant to be a plug for the Spectra - the is a fun detector if there's not too much trash around. Not to mention the is light as a feather - unlike the Spectra. I could swing the BH all day (it's easy to swing too fast). I just wish it had a dedicated pinpoint mode - I end up with holes that are BIG.

Thanks for the reply,
John