SD2000 Chips

[Woody.au]

A few people have worked out most of the chips on the Minelab SD2000, can others fill in the blanks? The SD2000 is still the deepest detector of the Minelab range. The one thing that im sure is worth modifying is the P & N channel FET front end, the next IC in line that is a matched transistor pair.
All these parts are 10 year old technology and better parts must be available.

[Qiaozhi]

A few people have worked out most of the chips on the Minelab SD2000, can others fill in the blanks? The SD2000 is still the deepest detector of the Minelab range. The one thing that im sure is worth modifying is the P & N channel FET front end, the next IC in line that is a matched transistor pair.
All these parts are 10 year old technology and better parts must be available.

What you need is one of these -> http://www.maplin.co.uk/Module.aspx?...ATLAS&doy=23m8

[Woody.au]

Just done some more measurements and found that the front end is a P @ N channel J fet long tail pair feeding the LM394 dual NPN current mirror setup.

Minelab made a poor effort designing the front end but maybe that was cutting edge back in 1994.

All the front end can be improved 100% just by changing to newer components. The one IC that has be stumped is the 16 pin chip in the audio stage, is it a designated audio IC or is it a VCO? The SD2000 has very low audio output maybe 200mw so it could be an opamp arrangement ...more detective work required.

[Stefan]

Hi Woody,

About SD2000 chip part numbers. Had problems with the MOSFET on the input to the main preamp. Was able to fix this and know actual part number. Will pull covers off box and confirm part number and location as per your layout schematic. Will do it over the weekend and post reply. At least one chip less in the puzzle.

Regards,

Stefan

[Woody.au]

The front ens fets are P Channel ZVP4105 abd N channel VN2410 and there must be better versions of these J fets around now.

I have the chips numbers for the other board as well and I will post it except for the 16 leg audio stage device.

I also have nearly finished a track layout for this detector as well.

[Stefan]

Hi Woody,

As you know the VN2410L is a relatively high voltage N Channel MOSFET 240V . There are plenty of better MOSFETS in the lower voltage ranges but completely different story when you get up the 240 volts and beyond and use it for small signal applications.. Blew it up 3 times on my SD2000 when I was playing around with different coils. Can't use a lower voltage one, not game enough to use a higher voltage one. Stick with the beast I know.

Regards,

Stefan

[Woody.au]

I think that blowing these up is more likely a current problem rather than voltage, the input is clamped via 2 X 1N4148 diodes so I do not think voltage is the problem.

[Woody.au]

Here are the chips from the other SD2000 board, soon all will be revealed, there really is not that much difference in the newer detectors except for a micro controlling timing and clock functions, no wonder Minelab grind off the chip numbers, must be scared somebody might reverse engineer their circuits.. lol

[Unregistered]

Woody,

I have just looked at the VN2410L MOSFET SD2000 and noticed that the drain or source is connected directly via a low ohm resistor to the signal line on the coil plug. This is why it has to be such a high voltage. I may be totally wrong but I think that the MOSFET is used as a gate and is only turned on during the sampling periods. I am unable to find the two back to back diodes as per the traditional circuits. Otherwise it does not make sense to use such a high voltage rating MOSFET. Have you traced out this part of the circuit?

Regards,

Stefan

[Woody.au]

I have not traced out the FET area but I have done the Matched pair in the second stage and the input on pin 2 connects to the reverse connected diodes.
If the J fet is just a gating device then there are better fets with just as high voltage rating and lower RDS values. I will need to sus out that part of the circuit.

[Stefan]

Woody,

The reason I mention this is that Candy in his patents always shows gating MOSFETS and never back to back diodes but does show the loading resistor across the coil. I think the SD2000 also has some means of utilizing/ retreiving some of the flyback voltage for power supply use/ and for clamping the peak flyback voltage. Good luck on your circuit tracing. Hard to do that with all the paint sprayed over the board.

Off to bed for me.

Regards,

Stefan

[Woody.au]

what paint? lol

[Altra]

Possible chip

Woody,

The 16 pin chip maybe a LM13600 or a cd4046, both can be configured as VCO circuits. Keep up the quest.

Mark

[Delbert grady]

well done

this is great stuff

[Woody.au]

The audio chip vco/opamp?? 16 pin dip still has me stumped except that pin 5 is Negative and pin 12 is positive pin 9 and / or 13 are inputs ... That must narrow the field down a little.