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Topics - woody

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Technical / Inside the GPZ7000
« on: October 02, 2016, 12:17:41 am »

The soft start or current inrush protection mosfet has burned a hole straight throng the circuit board.

This is starting to happen on older detectors, the reason could be just thermal cycling or metal migration causing the failure.

The small part that burns out is the Fairchild 455 mosfet, it is pictured on top of the white transformer core, the replacement is a 40 amp mosfet as shown with its 3 legs soldered to where the small
device was located.  The lower the on resistance as in the more amps it handles the better.

The FET that i used is a 100 volt rated 40 amp N channel mosfet but any high current mosfet will do the job, I left the legs on the set long as to make the connections easier to see.

This circuit board is not repairable as the power was left connected to the detector after it failed. The message here is to remove power from the detector if it stops working or more damage can be caused
making the detector unrepairable.

Technical / Isolating the input gate switching mosfets from signal ground.
« on: September 19, 2016, 01:03:48 am »
In the GPX series detectors the gate drive to the input gets is directly driven from the ADG333 via a BC857 directly to the gates, my take on this is that the designer tried to get as much gate saturation as possible lowering the conduction resistance of the fets. To get lower input noise and less gate capacitance to ground it is advisable to cut the track from the emitter of the 857 and add a smd 10 ohm resistor in series. This value can be played with but take it too high and the Fets may get hot due to resistive losses. On small gold tests I gained near 10% extra depth performance on tiny gold of 0.01 gram. Also a reduction in 1/f noise possibly by reducing saturated carrier electron storage but one would think that the long time duration between transitional states would negate this effect.  Less capacitance = more initial signal input. As i do not design mosfets it is a guess why the noise performance is better, I just observe the effects and take advantage of the circuit improvements.  Maybe optical or galvanic isolation is the next thing to test. So far the modded GPX detectors work much better than the SDC2300 and the GPZ7000 on most gold sizes subject to ground conditions.

General Discussion / GPZ7000 Video.
« on: July 29, 2016, 07:17:18 pm »
I did a video on initial impressions.  More to come.


How to repair faulty detectors / Faulty gpx lcd displays
« on: July 23, 2016, 01:28:21 am »
No display?  Most people blame the atmel micro on the board, it is not that chip.  If the display stops workingit is the the lcd itself. The very thin glass on the leg to board area can get fine hair line cracks and the display dies.

Displays are available through the manufacturer in France. Je-An  or the complete module is available in China for $100 usd. I tested some Chinese modules and they are 100% perfectly ok.

How to repair faulty detectors / Crazy fault in SD2000 detectors
« on: July 23, 2016, 01:22:04 am »
The detector is deaf as a post, it will pick up the side of a car and not much else.

First check the n channel fet near the coil connections, these fail due to metal migration in the semiconductor layers. 

Near the lm 394 ic on the input there is a 68 pf capacitor that is leaky, that is that it still measures like a capacitor but it starts becoming resistive, i have found this capacitor to fail on countless sd2000 detectors. It s located near he 4093 ic that controls the gate timing of the receive fets, it is used as a timing delay to give a small delay before turning on the fets after the end of the transmit pulse.

For sale and swap / Gpx4500 fully modded for sale
« on: July 22, 2016, 01:33:03 am »
I have a gpx4500 for sale, has the variable gain and variable frequency upgrades.
Message me for details.

For sale and swap / SD2000 for sale SOLD
« on: July 22, 2016, 01:29:04 am »
I have an sd2000 that is for sale.. Message me if you are interested.

After testing so many boards and trying out new settings to specific customers orders and can now say that obe board does not fit all detectors.  Boards that were created for the GPX4500 do not work on the GPX5000 due to the different input gain profiles of each detector. I was baffled as to why the input stage gain was only a multiplier of 33 and the GPX4500 has a gain multipier of 47.  It is easy to figure out, if you measure the resistors on both detectors you will find that both detectors have an inverting input connected to a 10 ohm resistor while the feedback resistor in the 5000 is set at 330 ohm and the 4500 is set at 470 ohms. When compared side by side in normal mode the 5000 shows significant depth loss on most solid gold targets. The point is that the 4500 is a better deep gold detector in both enhance and normal modes. So why is the 5000 taking a hit in the gain of the first input stage?  The answer is the fine gold mode. Fine gold uses an output pulse that is much the same as enhance but what is differerent is when the receiver comes on in relation to the transmitter turn off and ground decay. I would be thinking that having the receiver turn on in fine gold with similar front end gain of a 4500 would cause too much residual ground decay to get into the detector and make it noisy. So the cure was to use less gain but this causes the other modes to lose performance. It is very simple to test this and prove it by using a 4500 and 5000 and trying depth tests by using a test bed with buried objects. Apart from this difference between the detectors one could increase the gain in a 5000 to match the deep gpld performance but fine gold would become noisy. The only other way is to use a variable gain input stage so you can run as much gain as the ground minerals will allow. We invented the low noise variable gain input stage some 5 years ago and have fitted well over 1200 detectors with this sub board. The next phase is nower noise input stages that can make use of the low impedances of the coil and low ohmic resistance of the input back emf blocking and conductance Fets, All the later model detector use the standard low noise AD797 as the input stage but after some observation i discovered that the very low noise of these components could be made even better. The 1Hz to 10Hz noise specification is a lot higher than the higher frequencies that the ic is designed for, it has very low noise of 1nv/hz but not at the very low frequencies that the pulse induction detector looks at, the AD797 jumps up to 7nv/hz at these low frequencies and as this low frequency component drive the integration stages it seems that some sensitivity can be lost in the noise. The mission was to keep the noise floor under this level and keep the low frequency components under 1nv/Hz at the critical 1Hz to 10hz range.  Well it has been done with a choice of 2 sub boards 1 of 0.82Nv/Hz and one of 0.52Nv/Hz.  The greatest trick was to keep the slew rate very high,dampen any overshoot and keeping common mode noise under control by using a differential 2 stage amplifier and converting back to single ended output.  The whole design was built from scratch and it is a serious upgrade to install in any pulse induction detector, be it a SD2000 or later detector.

Information on the new developments / Latest mods testing
« on: April 28, 2016, 01:38:27 am »
Compare to the standard gpx5000 video

Information on the new developments / Testing standard gpx5000
« on: April 28, 2016, 01:35:45 am »
Done this as a reference to compare new mods.

Today we went to Talbot to test the latest upgrades, the video can tell the story better than words.

Under certain conditions (fully charged LiIon battery, unit switched off and back on in less than 30 seconds), as the internal voltages ramp up, the FET Q108 can be turned on for a few milliseconds and get destructed by the remaining charge in C145. This can happen to 4000 and 4500 detectors, if it happens to you then most likely there will be a burned spot on the bottom of the circuit board. The transistor is a BF820 , you can replace the transistor but you can blow it again by the same method as switching the detector on and off too quickly.

If you have an older 4000 or 4500 we can carry out the factory mod that will stop this from happening. It involves increasing the emitter voltage by adding smd diodes and one resistor change to increase the current through the transistor to overcome the voltage drop of the series diodes.

Note... The transistors used in the gpx are made by zetex, now called diodes. The transistors are not normal types but low saturation voltage types, they are rated at 20 volts at 3 amps.

False information / Other Forums
« on: April 02, 2016, 04:07:11 pm »
I have not read any other forums for maybe close to 24 months, but today i went and had a look at some of the forums as i was asked why i stated certain things on some other forums.

Some person /people or group are indicating that they are me and causing trouble, these people need to be made aware that if they continue to to cause trouble then it might be necessary to have the situation referred to a lawyer that specialises in bringing these people to account.  If you see any postings on other forums indicating that it is myself please ignore the content as i do not post on other forums except for Geotech, and maybe only 2 or 3 posts a year.

It is bad enough having my customers telling me what is told to them by detector dealers, you know the dealers that want you to buy a new detector and make them profits.

Things like, "Mods do not work"   Better tell the formula one teams to stop modding their vehicles...
                  "Mods void your warranty"   Saying this is in contravention of the trades practises act.. it is not true and not enforceable, this was tried on in regards to GMH trying to wiggle out of warranty obligations when new vehicles were modded by the Holden dealer team special vehicles business. Mods do not blow up a detector or cause any more stress on the electronics than if it was modded or not.

The public must understand the detecting industry, it is full of self serving nasty types of people, they will be a friend to your face and knife you in the back, 99% of prospectors are really nice people but there are some real nut jobs out there, some of the worst back stabbers are some of the detector dealers, they will say and do anything to stop you modding your detector and want you to buy a brand new detector, except that a modded older one can be many times better than anything that is new on the market.

The big companies "HATE" any form of upstart competition and use their financial clout to reduce competition or "ANYTHING" that can affect their profits, the industry is a "DRIP FEEDER" and by that i mean it is just a slight change between one model and the next, the functionality between detectors is much the same, you could look at it this way, a GPX5000 is just a modded SD2000, the base functionality is just the same. There are many ways to skin a cat and at the end of the day you have the same skinned cat.

As for warranty issues... I warranty my work for "5" years, fully transferrable.

And our mods beat the pants off a standard detector... and that is guaranteed.  The new mods that are about to be released even more so..

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