SMT Bandito Info/Build

[Silver Dollar]

Well I fired up my Bandito II SMT today. The first problem was a tiny TX (600mv) I had installed a 12K instead of 1.2K
(their wrong in my bag). I got that solved but now I do not have any negative voltage. It reads 0.5V positive. Hmm
I'll have to do some troubleshooting... I wonder if I loaded a 3906 in that Spot that was mislabeled?

I saw some distortion on the TX sine wave so kept increasing the value till it went away. I ended up with 2.49K and the
wave is bigger than the old Bandito.

[Silver Dollar]

Well I've found the 442 is used for the pinpoint function (and it has a 20 meg like a mod I showed) so what is the 27l2 for?
I assumed the 27L2 was CMOS so would hold the ground longer before bleeding off....

[Silver Dollar]

Oops the transistors have not been verified yet. I need a scope to see the
markings as they coated the board with clear spray and it's hard to read.

The TX is 2907 and one other is too.

I'm finding some funny readings too. There are no 4.7uf caps and the 358 resistors
seem to be 100k and 1k. The caps are 100n and 10n?

The resistors on the 308's appear to be 840k (1meg?) and 10K (instead of 47K) but the
caps are definitely 470n but 10K and 470n isn't right....

The lower string is the values I found in circuit.

[Koala]

Noticed TR6 is a 2n2222 instead of 2n3904 used elsewhere

2n3904 is a higher speed and lower noise device is there any reason that the 2n2222 was used other than availability ?

[Silver Dollar]

Here's a better schematic for the original Bandito. I fixed the pin numbers and changed to the 7660
for the negative voltage.

[Silver Dollar]

The TX on that Bandito is pretty wimpy;
10.4 khz
3.72v
7.78v Peak to Peak

Looks like RX has 0.01uf plus maybe one on the pcboard too.
TX has 0.015 uf plus 0.015 uf...

I also got the parts for the SMT board from Mouser today. It's almost done!



I did get some parts so can make it 99% to the schematic.

[Silver Dollar]

The bandito I have is interesting. It's a rev B board and has these components on a substrate;
LM308
LF353
LM358
LM393
27L2
7660
4024
4016

OFF the substrate is a LM2930-5 and a circuit with a LF442 in a dip package.


The GEB has a 100k trimmer to ground then a 100k 10 turn with a fixed 100k across it.
The sens and Disc pots are 100k.


Maybe something like this? I'm not sure where the 442 is though;


The negative voltage on this board is -4.4V. The batteries are paralleled with reverse diodes on the plus side.

Here's a picture

[Silver Dollar]

Well my Bandito came in today it's cool! I set it up and air tested a screwdriver to 12" or so.

I was reading that the Bandito found more trash (than the older models) so some were adding 90 degree Disc to it.
So I started working on a possible mod to allow 120 or 90 degree Disc;



I had a thought too about the center tapped coils. If you use the beginning wires for the coil and ground the ending
wires then the outside of coil will be ground so it will have some self shielding...

[sled]

Hmm I thought in general MD stuff was cheap and plentiful over there.

unfortunately not, a tesoro silver v2 goes for 500USD (new) in Switzerland/Germany. Problem is that Tesoro prohibits seller from the US to sell to Europe, so prices here are rather high. Luckily there are some black sheep in the US who sell to Europe under the table

Prices are horrible: http://www.abenteuer-schatzsuche.de/...oren:::72.html

[Silver Dollar]

Hmm I thought in general MD stuff was cheap and plentiful over there. Here prices were very high
but seem to be dropping a bit lately. I just missed a Silver Saber last week. I bid $110 and it sold
for $112!

I'd use mesh screening for a shield but thought it wasn't needed with a center tapped coil?

I found some brass screening that soldered great! Other stuff seems to be plated with pot metal and
is tough to solder to...

If you start with 2 wires and short those 2 together that would be your common ground point. Then wind
the rest of the coil and the 2 ends are your coil points. That way both coils see the exact same voltage
and can eliminate common mode noise.

That epoxying as you wind is the way to go. I wind then tie with dental floss then use superglue to hold them
together but it can make adjusting later a bit difficult. One coil I used tye wraps and superglue then couldn't
get the wraps off! Need a big housing for that coil...

[Koala]

Wound some coils for my IDX don't have any problems with stability. Use a jig that epoxies the wire as it's being wound.

Do have a problem with using a space blanket for shielding. works excellent to start with but degrades with time.

Never wound a bifilar something new to learn does not look that hard. (which ends connect to which for the center tap.

Original coils are also graphite shielded as well as center tapped.

Prices in the UK for Tesoro are bad. A silver sabre on ebay just gone through for just under £200 ? Original coils do seem to lack depth also but they do run super stable.

[Silver Dollar]

I think all the Tesoro projects on here use the same coil. The one for TGSL should work on Bandito.
I made a few of them before moving on to the Minelab coils. It's like 100 turns and 105 turns, though,
I found the wire I got off Ebay wasn't really the AWG it was supposed to be so my numbers were off.

To tell you the truth buying a coil will be much cheaper in the long run. I got $12 worth of wire, a $15
case and $32 worth of epoxy. The inductance changes daily too so it's hard to pinpoint just what you made.

I have at least 2 sets of original TGSL coils and 4 or 5 other special winds but none in a housing yet. Center
tapped is the way to go though. I found an ancient GS schematic that showed a center tap. You don't have
to worry about shielding if you center tap. You want to wind it bifilar so get 2 coils of wire to make it easier.
I built a jig with a plate with the coil form on it and a 2x4 with the 2 spools of wire at one end and coil form
at the other. It's easy to wind that way! The front end only makes sense with a center tapped coil.

On grounding the case, originally it was better not to then somehow it changed and everybody was grounding it.
The Tesoro's in the old days were in a metal case, then they switched to plastic, I don't know if there was any
shielding in it. I''l look in the Bandito as soon as it gets here.

[kt315]

The Eldorado and Bandido are very similar.

Gold Mountain Tech King Cobra has two tone sound, Accept Reject Notch filter, also you can add Surface Blanking adv like in Royal Sabre tesoro if you want.

good luck

[Koala]

Found this thread on the mods forum. The Eldorado and Bandido are very similar. Noticed that a performance increase in all metal mode if the board is in a metal grounded case or at least a lined with foil. Link.

Doing some research at the moment to find the best coil specs for a 27DD. Thinks it's better to go for a center tap same as original to keep the phase shift the same.

Tesoro detectors seem to be popular on the www.teknolojiekibi.com forum site some good results with home made Eldorado. Google does not work well on my machine and bings is slow going.

Waiting for parts from China to arrive while this is happening I will finish the Mouser list off and get them ordered.

[Silver Dollar]

Well my real Bandito will be here Thursday or Friday so while waiting I've been looking at some of the other
Tesoro MD's and wondering why some are touted as going deeper and some have sweeter tones as they are
very similar. The newer ones seem to have no restrictions on depth whereas the older ones "hit a wall" and
wouldn't go deep even on big targets.

In looking at what mods could be done to try and improve the Bandito I found several that would be easy to
try. One is to leave the 4066 out and use the opamp from the battery circuit and a 4053 to use both polarities
of the input signal. A little tough as the parts are surface mount but I have a scrap board with a 4053 on it
that I can cut up to make a tiny daughter board.

Adding the Minelab oscillator will put 150 ma into the coil verses 32 ma stock. With the AB+C mod it only consumes
5 ma (not sure but I think stock is 2 - 3 ma). That will get a lot of signal into the ground but might change the
Bandito's characteristic of working great in very trashy areas. It's not clear what in the circuit allows this feat.

The negative supply might need addressing too but most changes there will increase current consumption a bit.
I have an idea to make a Golden Saber and use plus and minus 12v on it to see if it makes any difference.

Well here's a schematic with some of the changes for you to peruse;