Minelab SD2200 problem!

[Mechanic]

That will be your problem.
It all depends what is running in your area. They don't like switching power supplies!

Good luck and have fun with it.

Cheers Mick

[plboy]

Hello colleagues,
I have problems with the SD2200v2 - it does not work stably and has no threshold and sensitivity.
4 channel potentiometers have been rotated by the previous owner,
I need information and diagrams for setting up the 4 channels,
Thank you in advance

[Xtrem]

Far from interferences ,the problem still exist. Plboy i have exact the same problem.
Is the circuit similar to SD2000? I know the 2000 has 3 channel , the 2200 has 4.

[plboy]

Be similar to sd2000. Only ch2 works for me, but the sensitivity is very low

[Mechanic]

A common fault on the 2200 is an smd ferrite inductor right next to the RX input wire. It gets a bad connection or goes open cct. Put a 0 ohm (short) in its place.
The input to the preamp, ie the front end fets, is the same as the 2000, apart from the 2200 using a 2sk217 N channel fet. That fet is no longer available, but there are alternatives, =>200v, low capacitance, lowish resistance(1 to 20ohms). Do the ferrite first.

For the trimmers, only adjust them if they really have to be adjusted. Before adjusting, measure the resistance of them so they can be set to what they originally were.
You need a small ferrite magnet, like from an old speaker(about 2" diameter, not 10" ), with all metal removed. Raise and lower the magnet in the centre of the coil, you should hear no response.
Disc channel needs to be set with a DD coil and oscilloscope, but will work fine without it unless you actually want to use the disc feature.

If sensitivity is the issue, then the trimmers have nothing to do with your problem, well not yet anyway! Trimmers are for cancelling static magnetic fields only.

Cheers Mick

[plboy]

Hi Mick,
Thanks for the fast answer.I haven't touched the trimmers at the moment, although they were rotated by the previous owner (it can be seen by the lack of paint), if necessary I will adjust them further at the end.
The device worked and had sensitivity, but the threshold became very strong - this is the main problem at the moment.
Only on Ch2 it works at normal threshold but is not sensitive. I have 2SK216 and AD797, I have 190vDC on the diode, the input smd choke works.

[Mechanic]

The 190v you have, was that measured to batt- or detector ground(batt+)? 190 is a bit high if measured to ground, but perfect if measured to batt-.

On the audio board, measure at the test points. You should basically get 0v if measuring with a multimeter. If you have a scope, set to 5 sec/div, 2v/div, you should see a response when you wave a target over the coil.

The loud threshold you hear indicates there should be a dc voltage offset on ch1 at those testpoints(assuming I have the channels labelled correctly). If not, the problem is further forward. I have seen residue under one of the large 1uf poly caps cause the threshold to do this and create a slight dc offset.

Try a little bit of hot air, dose sit change things?
Are +-5v rails correct?



Cheers Mick

[plboy]

Yes 183v to GND (+Batt), +5v and -5v are OK. There was a problem with the 2sk216...
now there is some sensitivity but there is a lot of interference in the workshop and I can't judge or measure Ch1 and Ch2.
In good weather I will go outside to try it. Isn't zvn4424 better than 2sk216?

[Mechanic]

zvn4424 will work and is quite good. The 216 datasheet is lacking a lot of specifications so it is hard to make that judgement and due to their non availability I've never bothered testing them under the microscope.
Yes interference will be a big problem in the workshop. Try the magnet when away from interference. The GB channel, you may need to set that one using your scope as the gain on that channel is low and it can be hard to hear it.
I think you will mostly now have this detector sorted out.

Cheers Mick

[plboy]

Hello,
The problem was with a bad solder with 2sk216, the input and output capacity are also important.
If there is resin or contamination between the terminals of 2sk216 be sure to clean.
Thank you colleagues, stay healthy.