Bandido 2 Modified

[Merc]

I'm still trying to make slight changes to my Bandido2. The discrimination is working now but a nickel was getting discrminated at about where the number 6 would be on my dial. I'm use to a nickel dropping out at about4 on every Tesoro that I have so I decided to adjust the circuit somewhat. I experimented by paralleling other caps across C9 which is originally 100pF. I knew I needed to shift the phase of the TX sine wave one way or another but I wasn't sure which. By adding a 150 pf across C9, the nickel coin dropped out right about where the 4 will be if I ever get my front label printed. So, I changed out the 100pF for a 250pF I found in my junk parts and the disc seems very similar to my other Tesoros. However, my Bandido 2 will even reject a quarter at max discrmination. I'm not sure if thats normal.

Now if I can get the battery test working. Using the original values as shown in the original schematic, I get a loud tone for 3-4 seconds with 9V input to the board. I still get a somewhat lesser tone for 3-4 seconds with 6V fed to the circuit. On my other Tesoros, it seems like the tone length and loudness varied with battery voltage. Looking at the Bandido battery test circuit, there is no way for the length of the test to vary. The voltages tied to the timing components, C7 and R12, are fixed voltages. Regulated +5 at the top and the negative voltage at the bottom that is derived from the positive supply, let's say it's a fixed -3V. That's all that control the length of time that the 4066 switch is turned on connecting the test circuit to the audio output stage. The battery voltage is divided and input to one of the inputs of the op-amp which will affect the voltage output that gets switched out through the 4066, but than won't affect the length in any way.

According to the Bandido II Umax manual on Tesoro's site, As the battery ages, this sound is less intense and fades out more quickly.

Perhaps someone out there with an original Bandido II uMax could test there detector and see how it's supposed to work because something just doesn't seem right about that circuit.

Merc

[Merc]

Here is a picture of my completed PCB. I'm still not sure that my ground balance contol is proper. It can ignore a small piece of ferrite but only with the ground balance control all the way at one end(pot measures 48K). So I chaned the 180pF going into gb control with a 300pf. This makes the ferrite null point closer to the center of the pot. I'm not really sure if this correct but it seemed better to have some range to either side.

The discrimination is good but I would still like the point of discrimination of US nickels and gold rings to be at about 4 on the dial instead of 6 or 7 which is what I had to start with. I've started to wonder if maybe Tesoro uses logarithmic or audio taper pots in there units. That could explain the difference. Studying the Tesoro Silver Sabre II schematic, I see that it uses a 100K fixed resistor across the low end of the 100K disc pot. I've tried this and it does help shift the discrimination in the right direction and my unit no longer rejects a US quarter at max discrimination.

I'm still needing help with the battery check on this unit. I can't see no way for the battery test length to vary since the timing components are charging with fixed supply voltages. The intensity of the test tone varies with supply voltage on my unit, but not the length. The manual says both change with battery strength.

Merc

[Merc]

More pics of pcb in case.

Merc

[keith777]

WOW making your own detctor something i could only dream about. i hope all the hard work you have put in to this project pays off for you and please do keep us updated on all of your progress on this machine. cant wait to see the full end results.............

[Merc]

I have only tried my detector in my back yard but I was able to find a cheap child's ring and a small heart from a child's pendant. The discrimination is very good. The sensitivity is just average. It will detect a gold wedding band at about 7-8 inches. Most coins around 6-7 inches. These are air tests only. The all metal mode is working pretty well after adding 20Meg of resistance across the Auto/Normal switch. This gave some input to IC6a with the switch in the Normal position. Without the 20Meg, the input to IC6a is floating while the output is still connected to IC6b and it seemed to be adding sporadic noise to my all metal mode. Other Tesoro designs have something between 12Meg and 100Meg in that part of the circuit. 20Meg gave me a slow re-tune while pin-pointing that works for me. I wished I had used a larger box. The pots I chose were full sized approx. 1" diameter types and the front panel was really crowded. Here is a pic of the unit which uses the rod from my old Silver Sabre 2.

[keith777]

looking good. im sure you will sort all the niggles out eventually.

[ivconic]

Merc... good work! Nice and clean!
Could you void bulky wires? Although original Tesoros are even more shaggy!
Good job!

[Merc]

Ivconic,
I could certainly shorten some of those wires. I already trimmed the coil wires and the wires to the ground balance control. The others are still the original length I used during testing. I was in a hurry to see it work and haven't cleaned it up yet.

Merc

[ivconic]

Your work is clean so i think bulky wires would not cause any extra problem. I opened Bandido II, Eldorado and Silver Sabre, so far, and i saw pretty bulky wirements in those originals too. However...those were in metalic enclosures...except Bandido II which has "I___I" shape metalic holder that can act as good shielding also.
Speaking of sensitivity..; with coil on your photo you can not achieve some extra results. I had same coil with my Bandido II. Poor performances too. But once i connected my DD handmade on original Bandido II...! Wow! Extra good performances! That was the same handmade DD coil explained in "Tesoro Golden Sabre" thread.
So...you have good machine for sure and now is time to make good coil. I suggest you to do that and than i am sure you will be very satisfied with your detector. Try and see.
Regards!

[woody]

did you get the battary check working there are so many schematics for the bandido who knows which is working or not
have you tried
adding R24 68k
change R11 200k for 2M
swap R8-R9
put a jumper on j1
put a biocolor led on j2

[Merc]

I'm still not happy with the battery check. I can't see any way for it to work properly the way it's designed on the schematic. I was hoping someone on this forum might have an original Bandido II uMax that they could check. I'd like to know if the length of the test signal varies with battery strength as the manual suggests.



Woody, which schematic are you looking at that shows the different resistor values?

Merc

[woody]

found it here
http://www.volny.cz/kachlik.jan/dete...ido_II_sch.pdf

[woody]

forgot to add got it from this site
http://www.volny.cz/kachlik.jan/

[Merc]

Woody:
I still have not figured out this battery check, but before I build another one, I will.

Ivconic:
You have inspired me try and build my own double D coil. I will probably follow your recommendations in your TGSL instructions. I am going to cheat a little by buying an enclosure from here: http://www.hayselectronics.com/parts.htm . I have ordered the housing designated "A". The price was only $14 USD. Once I have it, I'll trace the shape out on a piece of wood and use the dowel pins as you did. Simple I hope. Number of windings could vary a little since the diameter is probably not identical to what you made.

Merc

[silverdog]

Hi Merc

What a great job you have done on your Bandido II - did you finally get everything working ok ?
Would love to see some more pics if possible, I fancy having a go at a Tesoro soon, you have inspired me !!

please update us

[Merc]

It is working. It's nothing out of the ordinary. I still don't believe the battery test is working as it should, but I quit worrying about it. I've moved on to my second detector building project, a lightweight version of the Toltec 100.

Merc

[driscoll]

"I'm still not happy with the battery check. I can't see any way for it to work properly the way it's designed on the schematic. I was hoping someone on this forum might have an original Bandido II uMax that they could check. I'd like to know if the length of the test signal varies with battery strength as the manual suggests."

Hi Merc,

Yes, i have an original µMax Bandido II and the length of the test signal varies with battery strength.

These informations are in the manual.

Regards

[Merc]

driscoll,
Could you examine the circuit in your detector and compare it to the schematic on this forum and point out any differences?

Merc

[driscoll]

Sorry Merc, but the original µMax Bandido II use surface mount components. It is not easy to examine and test.

Bests regards.