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Treasure Hunting & Metal Detecting Forum Message Boards - Detector Hunter Whites Minelab Tesoro XP > Tech Talk > Modifications, Do It Yourself & Repairs (Moderators: Eugene52, xavier, GoldDigger1950) >

Minelab XS2A-Pro Board fault.

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chopz54 Topic starter

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	Minelab XS2A-Pro Board fault. « on: March 29, 2012, 06:51:43 am »

I have got a Sovereign XS2A-Pro which was completely dead,opened it up and found someone had removed the O-crystal out -so have replaced it...Now I have working threshold tone!! But nothing else!! But thats a start!

Next step- I did a voltage test (Neg-battery & Pos to the 3 pins) on
what I believe are the 4 Mosfets? (see photo)
and compared the readings with another Good working XS2A-pros readings.
(both machines were switched ON and the readings taken from the board underside)

Heres the readings:

Faulty XS2A-Pro Good Working XS2A-Pro

MTP2955 0v 6.37v 11.03v 6.11v 6.21v 11.12v

MTP3055 6.38v 6.41v 1.78v 6.11v 6.21v 1.28v

MTP3055 6.23v 6.39v 1.78v 6.04v 6.20v 1.28v

MTP2955 6.22v 6.37v 10.98v 6.03v 6.20v 11.11v

As you can see I look to have a fault on a MTP2995 Mosfet? (arrowed in photo)

Can anyone enlighten me as to function off this and would a simple replacement
suffice? or could there a problem elsewere causing this?

Any help/advice would be most appreciated. Thanks.

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GoldDigger1950

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	Re: Minelab XS2A-Pro Board fault. « Reply #1 on: March 31, 2012, 02:34:33 pm »

A MOSFET is a switch. An electronic one that switches high voltage on and off when a low voltage is applied to or removed from the Gate terminal (depends on the channel type). The voltages you are reading are not DC voltages but varying pulses which can best be seen with an oscilloscope. You asked for an explanation. That's it.

The most likely problem is not the MOSFET itself based on your readings. It might be Q204, right next to the MSOFET in question. Or it might be the digital circuit that feeds the gate transistor Q204. If you are willing to use a "shotgun" method versus actual troubleshooting, replace the MOSFET and Q204 at the same time. If that fixes things, great. If not, you have to start looking further "upstream" to whatever devices feed Q204 and compare them from good machine to bad machine. One thing is for sure, it would appear that an oscilloscope is something you should either buy or rent.

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	Re: Minelab XS2A-Pro Board fault. « Reply #2 on: April 01, 2012, 07:35:39 am »

Thanks for that GD. A nice concise answer Great

I have some Sov w/diagrams and the way its wired it seems logical that Q204-- BC368 could be causing the problem....I will see.

Thanks again.

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	Re: Minelab XS2A-Pro Board fault. « Reply #3 on: April 02, 2012, 05:29:26 pm »

When a MOSFET fails, it becomes a "nail" as we electronics types call it. In other words, a dead short circuit. Thus, they are always fed with a gate transistor to protect the rest of the circuitry. Those gate transistors can sink a serious amount of current but sometimes a spike will sneak through to them and destroy them. Change both our at the same time just to be sure.

In a PI metal detector, those voltages that you saw on the MOSFET Drain (you have three terminals - Source, Gate and Drain) were a DC average in a circuit where spikes as high as 400v are sometimes seen on an oscilloscope so be aware that there are very high voltage spikes present. Not dangerous to you but a careless touch or an accidental short by a meter probe can cause problems elsewhere on the board. Most of the other chips on the board will be CMOS to save power and use less battery juice. They are very sensitive to damage by voltage transients or spikes.

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