Minelab SD2200 problem!

[ivconic]

Need help. Need guidelines to locate the problem.
A man send me brand new SD2200. Looks like never used. Switching ON with coil connected, machine is producing pretty constant wobbling audio. Nothing else. Only Tone adjustment reacts, no other else. Without coil connected when switched ON it starts to act like everything normal. Treshold and Tone adjustments reacts and makes difference in audio so as Tune button when pressed (only first time after switch ON).
There are two brand new coils and machine acts the same with both coils. Battery is brand new and charged to 6.5V. Drain is small...when machine switched ON voltage on battery changes from 6.5V to 6.4V....
All connectors checked from eventual breaks or shorts - good condition (brand new).
Coil measured and seems there are 2 coils inside; 0.4 ohms and 16 ohms.
I just recorded 3 MP3 files using microphone closed to earphones. 3 cases; first one is audio when coil connected on machine. Second MP3 file is when coil connected and Tone pot turned and third one is audio when coil is not connected....
So...
Damn enclosure is so tough and all inside is packed pretty awkward - not desirable to frequently open and close. To void that i would firstly like to hear your suggestions about present issue. Hints, tips, suggestions will be highly appreciated!
There is SD2000 schematic on these forums....not useful in this case cose i already compared it with what i saw inside SD2200 - lot of differences...
Ok...
i am restless to hear suggestions and advices!
Regards!

[ivconic]

One more thing...yes.. TX seems to work. I used simple method - put ear on coil and hear clear transformer look like buzzing inside.
As already known; both pcbs are painted with some white paint....tough to follow traces and see all the components clear.
I want to check if there is some trivial problem and later to fix it or...if problem is more serious than i will send it back to owner and suggest him to send machine to some official service abroad (pretty painful solution for us here...). That's why i would like to void paint removing from pcbs...at least for now..

[eclipse]

Woody.au i think repairs SD's perhaps he can help.
Good luck !

[ivconic]

http://detectormods.com/

Yes, i know. Just send him email....

[ivconic]

I just checked this:

"...All these detectors have a FET that is mounted to the case of the detector. These are supposed to have 3 legs but this one has 2 legs. What happens over time is that any vibration or shock causes the circuit board to flex and as the FET is connected to the board by the legs and the body is mounted to the case there are large forces that try to move the component. This detector had a fault that when it was turned on it started sounding like it was trying to send Morse Code. It sounded like random beeps from the headphones. I had to unsolder the FET to find that the Gate lead had become detached inside the FET. This made it hard to spot by looking at it while still connected to the circuit board. In this picture a new FET is installed and the old one sitting next to it. Any FET can be used to replace it as long as it has a rating of greater than 250 volts and 5 amps. The original part is an IRF840. This fault is quite common in detectors that get bounced around in the back of the car...."

Just replaced fet in my device and nothing! Same behavior!
Damn paint! Can't remove it easy!

[ivconic]

Considering all what i have seen and checked so far; seems like it has certain current issue. When coil is not connected detectors seems to work, but when coil connected it starts "wobbling" and not reacting on commands (except tone command). This SD is first i see in my life so far, i don't have previous experiences at all. But looking numerous clips over the internet i collected some "experience".
But if it is current issue...than why i still hear usual buzzing in coil? TX works than? TX or any other stage draws some current and than provoke audio wobbling for some reason; most probably some faulty component..hmmmm...
Which one?
This is rather like Scherlock guessing, personally i don't practice that kind of "repairs"! But this case is special; i would like to void paint removing ( spit from me on Minelab account!!! ) and check if that was some trivial fault or something more serious...!
No answer from Woody yet. Australia is in different time zone, what's the time there right now? Maybe Woody is sleeping?

[ivconic]

Just got response from Woody!
I will check and replace what he suggested....

[WM6]

Just got response from Woody!
I will check and replace what he suggested....

Good news. Pls inform us about results.

One of my detectors (Imperator) had a similar problem. There was unvisible broken middle leg by one of voltage regulators.

I discovered this error with a slight tapping by plastic screwdriver on some elements on board.

[ivconic]

I still can not find fault! I tried many things. I did like Woody suggested. It was not a problem; suggested fet 2SK216 is ok, so as nearby VPN (ZVP). Also checked TX outputs 2 x IRF640 ....good also!
I had half day hard labor to remove damn paint from some areas on pcb. If it was not painted i think it would be much easier to locate fault! The way it is now...i am thinking to give up! Maybe component placement would help a bit, because i can not find which component is where!! Can not trace also because traces are painted too!
I am wandering; what the hell Minelab wanted to achieve with this paint!? Protection? From what? From servicing? The way it is now...with my recent experience (all day torture with it) i am sure i will advertise those machine in pretty NEGATIVE context from now on! I will spread the news among prospectors - NOT TO WASTE MONEY ON SUCH PAINTED TRASH, simply because it is not easy to service it later, when some eventual fault occurs!
I simply give up!
I will only report all this to Woody to hear his final opinion and than i will "close this case" for good!
No more "painted" trash in my workshop! PERIOD!

[ivconic]

Reading also Woody's pages so as some prospectors forums i see to many "common" faults at those machines (SD series) !?
I made a list of all "common" faults and today checked all on this one here! Ain't neither one of "common" faults at this damn machine!
Am i lucky man or what!?

[eclipse]

I've always wondered what MCU those devil machines have,
Ivconic do you have a clue what might be under the nasty paint?
Perhaps Freescale DSP?

[ivconic]

If i decide to open it once again i will remove paint from mcu and see labels. But that is only "if"! Right now i don't have such intention...At least until i hear final opinion from Woody or somebody else, who's dealing with SD series more often..

[WM6]

I am wandering; what the hell Minelab wanted to achieve with this paint!?

No more "painted" trash in my workshop! PERIOD!

I heard that Minelab intends to rename his company in Paintylab.

[ivconic]

I heard that Minelab intends to rename his company in Paintylab.

Luckily Explorer is not painted inside!
Sheeeeeeesh!

[ivconic]

Problem(s) finally solved! Pretty "uncommon" fault!
Cable from machine to battery was very bad,most probably already changed, because it is not original. And inside cable there are 4 coated litz wires...but very thin!?!? So...plus pole litz somehow broke and one litz probably touched earphone output (deja vu! same thing i had in the past with RH!!! )!!!
So...hmmmm!
To cut the story....i had a lot of hard labor today, replacing some burned components!
Now SD2200 is alive and kicking like donkey!
I performed some indoor checks and test and must admit it is pretty descent machine! Discrimination is accurate up to 60cm away from coil surface. Over 60cm it "see" every type of metal the same...
Most probably it will perform much different on real soil...
Must check it outdoor tomorrow..
Conclusion; after all troubles...it is not bad machine at all! It is pretty good and interesting!



P.S.
It is still nightmare for servicing!!!