GPZ7000 repair?

[bklein]

I have a GPZ-7000 that has very low sensitivity. It got worse over time to the point now a nickel is sensed only up to 3?. Anyone have any insight into this detector circuit or voltages that I can check to try and pin this down? It is not a bad coil.

[Carl-NC]

The GPZ has a sealed module in the receiver front-end, it is unlikely that you can debug it.

[bklein]

Yeah I saw that thing but I was thinking it was a TX module. Minelab says the two boards must be replaced in pairs - they are $4600 to replace. They said they tried to update the firmware and something got hot. That doesn’t sound right to me… I haven’t tried yet. Seems to function ok. Anyone taken TX current waveforms? I could compare to at least validate TX.
Guys are killing their GPZ’s with badly wired x coil adapters - maybe someone knows of one of these? (Parts source)

[bklein]

Well I looked at it tonight and you are right - it is an RX module - and it gets hot just being powered.
Not like the GP Extreme I fixed years ago - I now know this black plastic well - after I tried to get at the board of a CTX coil and it took all the components off the board when I pried on it.
The FoxMD guy in Russia might know how to get the plastic off without damaging anything but I sure don't.
So its a closet queen until I hear of a GPZ in a fire or someone accidentally driving their truck over one.

[ivconic]

https://www.grainger.com/product/SPE...-75-09-2-6NMZ6

It is a solvent... to solve your problem!
Beware!
It is a carcinogenic and highly flammable substance.
Wear an apron, gloves and goggles while you work. Work in a ventilated place.
Pour the liquid into a pre-prepared container with a lid.
I use a pot with a lid made of ordinary injected plastic, bought at the market. It turned out that this plastic is quite resistant to chemicals.
Insert module.
Cover.
Wait from 20 minutes to 20 hours (depending on the chemical composition in module).
Every 20 minutes to 2 hours (you will understand in time, it will tell to you by itself) check the strength of the mass on the module.
Poke it with a knife like when you check the roast!
You will notice that it is slowly becoming gelatinous.
When it starts to come off easily with a spoon or similar tool ... that's it.
Remove the module and transfer it to a similar container with cold water.
Return the rest of the chemicals to the original packaging and keep for the next opportunity.
Since a good part of the epoxy remained melted in that chemistry; I first strain it through a sieve or gauze or similar, before returning the liquid to its original packaging.
Store the bottle further in the basement, in a dark place with a constant temperature, preferably not above 15 degrees Celsius.
Let the module stand for ten minutes in the water and then start to slowly separate the mass with the same spoon, tool, knife.
The risk of chemistry is no longer high, you can work relaxed.
In this way, I "melted" many modules and many coils cast in epoxy. Some melted after 20 minutes and some took 20 hours.
It all depends on the composition of the epoxy (they are not all the same), on the age of the epoxy and probably on the concentration of methylene chloride itself.
In some countries it is a highly controlled substance, resticted, and cannot be found over-the-counter.
I don't know how things are in the country where you live. But if you can't find it any other way; look for in the army.
They use it when they remove old paint from vehicles, tanks, planes ... Find a connection, an insider ... to "smuggle" at least 1 liter.
I couldn't buy it in retail here. Only through the account and through the company. I managed somehow ...


P.S.
I found on Internet that that miserable neo-globalist toy costs $ 8K. And they're asking you for $ 4K6 just for the boards !!!
They really deserve to be ... you know what!
I would believe in the true minds and knowledge of the people in ML, if they designed that detector so that it can't break down so drastically.
Because for so much money, that is the least that a buyer can expect. So much for the mind and knowledge of these so-called "engineers"!
Such an overpriced product must have basic protection against the most trivial failures, such as bad connections on the connector,
short circuit of wires on the connector or similar nonsense ...
In a relentless race to grab as much money as possible; they have become so obscene that they no longer have scruples.
So it is possible that such a $ 8K detector totally dies in such a trivial way.

[bklein]

I can’t get the MEK products here. Maybe there are professional shops that do it? Also some of the compounds get rubbery with heat and can be pried off. I’m going to take my time investigating as I likely only have one shot at it.

[eclipse]

Post some pictures of the module. I've had some success with removing epoxy potted pcb by boiling in water.

[bklein]

Photo of module. It has several solder pin connections to the host board but I don’t expect any problems getting it free of it.

[eclipse]

You maybe better off just selling it for spares and repairs.

But If you'd try and risk it..

As a first step I would try a heat gun on one of the angles starting with 100..150..200 degrees just to check out the melting point of the compound, in the meantime poke it gently with a screwdriver.
You can also check this out with a regular soldering iron. The objective is to try and see how high temperature is needed to melt it. If it's much over 100 degrees boiling is not going to work.

There's also a liquid, that I have in the basement, which is very low reactive and hard to obtain but safe to use. RRS it's called. I gave one 1L bottle to a friend and he was able to remove pcb potting, but worked very slowly.

[ivconic]

Photo of module. It has several solder pin connections to the host board but I don?t expect any problems getting it free of it.

Black mass; is it epoxy after all?
Is it soft or hard, poke it with needle or knife and see.
Assuming it is hard and it is epoxy of the toughest kind...
I am afraid the methylene chloride is the only solution...

[bklein]

I’ve discovered there are quite a few companies that repair potted PCM automotive modules. I have to talk to them to see what their capabilities are. You are right, this looks like tough stuff to dissolve.

[Orbit]

I took off a lot with the smd component blower that module is a very small problem compared to the things I remove..Just one example removes the resin on the minelab vanquish 540 coil..

[bklein]

Wow, very impressive! Got any YouTube videos of doing this work? So use a temp controlled heat gun and a dental pick and work slow? What temp did you work with best. Will the boiling in water method work with this material? Are you foxmd? Not many on the planet that have these skills.
Another method I’ve discovered is sort of a micro sand blaster approach. He could focus on just the component area that’s getting hot…

[Carl-NC]

If Minelab did it the way I would do it, then the module is an MCM with die-level chips and printed thin-film resistors. If you manage to dissolve and remove the epoxy you are still sure to destroy the module. I would look everywhere else before doing this. Especially look at the TX and see if it's running full strength. Problem is, any troubleshooting is poking in the dark without another machine to compare with.

[bklein]

Yeah you are right! We have an X-ray system at work to check BGA soldering. I plan to use it to verify there is a replaceable component where the heat is radiating from. Even if I succeed with this I may not be able to determine what the part is after removing the epoxy… How to check the tx? Would a current probe check be sufficient or would there be another way?