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Guest Jennifer

GPZ 7000, A Look Inside

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51 minutes ago, Jennifer said:

In all fairness to Minelab, we have no idea how old this unit is or how rough it was treated. 

[...]

Dont judge the build quality without knowing the history of the unit.... :smile:

We have no need to know how old the unit is or how rough it was treated because in the video we can see the history we need.  I.e. how it was designed.  Which is poorly when it comes to this wire connection.  The ML design here connects some discrete wires to a PCB by use of a simple through hole and a blob of solder.   That's pretty much a design fail for reliability and ruggedness in gear that will be constantly be moved / handled.

There are lots of types of discrete wire to board connectors available and ML used none of them here.  Such connectors exist because otherwise stuff likes this happens. 

Given the label for the connection, "TXA"- transmit A, my (limited) understanding of the Russian narration, and the fact the box is open and under repair, it seems the failed / intermittent connection is pretty important.

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Guest Jennifer
2 hours ago, MDdetector said:

We have no need to know how old the unit is or how rough it was treated because in the video we can see the history we need.  I.e. how it was designed.  Which is poorly when it comes to this wire connection.  The ML design here connects some discrete wires to a PCB by use of a simple through hole and a blob of solder.   That's pretty much a design fail for reliability and ruggedness in gear that will be constantly be moved / handled.

There are lots of types of discrete wire to board connectors available and ML used none of them here.  Such connectors exist because otherwise stuff likes this happens. 

Given the label for the connection, "TXA"- transmit A, my (limited) understanding of the Russian narration, and the fact the box is open and under repair, it seems the failed / intermittent connection is pretty important.

Through hole soldering is quite common/the industry norm and the strongest method to attach wires to a board when there is no to remove the wires or use a pin header, molex etc.

It's not simply a wire through a hole and a blob of solder as you put it. The wire is tinned and inserted in the hole which is lined with a pre-tinned copper trace which has a round tinned solder tab on the other side and then it is soldered, usually via moving the board above a sheet of molton solder, this is called wave soldering. The surface area of the copper inside the hole and the solder pad give great mechanical strength once cooled. If moved during cooling, a week bond or cold solder joint (indicated by a dull grey finish, not shiny as preferred) can result, as it appears happened here. The above mentioned traces are chemically etched into the printed circuit boards and normally last the life of the board and do not lift.

In relation to our detectors moving, the relationship between the board and connection for the coil that this wire uses is relatively non moving, housed in the same case, they are static to each other, other than jostle from the wire shaking and as I'm sure they used stranded core and not solid core, again sufficient.

These two board photos are the solonoid boards from one of my M5's earlier mentioned. They adjust the engine VANOS timing by allowing or disallowing engine oil under pressure to change the camshaft position. Notice anything in the photos? Exactly the same wire attachment method... (on the little green printed circuit boards, orange arrow. The main board has pins but the bridging boards between the wires and solonoid leads are straight common through hole soldered to solder trace tabs).

I reckon Minelab thought if it was good enough for a $100,000.00 German BMW in the engine compartment, under the constant vibration of a V-8 engine, it was good enough for them, and I concur.

PS: I do concur it appears to be a cold solder joint that opened up the connection but that speaks more to an isolated one off faulty solder as the board transitioned over the wave solder table, not indicative of a bad wiring connection design.....

Note: There's a good chance that the soldering of these wires into the already populated (with components) and wave soldered board is a manual process and as a result was simply human error.

Just a guess but TX A is most likely transmit coil A winding.

Jen

IMG_2436.PNG

IMG_2437.PNG

 

 

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I have had detectors made by every brand fail on me. The more anything costs, the higher my expectations get for quality design and durability. Yet as a person who ran a service dept I can testify that is not reality. The best companies make good products, then use a feedback loop based on warranty submissions to improve those things that fail. As a rule this means buying first year product makes you part of the final bug check, with models made in the second and third years of manufacture becoming more reliable as engineering design faults and manufacturing errors are identified and corrected.

Loose intermittent connections and other intermittent electrical issues were usually the worst. Typical failure report by customer and works fine in shop. We sometimes spent days tracking down an issue that took five minutes to fix. You ever try billing a customer ten hours for a five minute fix? Fun stuff! :smile:

Interesting look under the hood - thanks Jen. Welcome to the forum MDdetector.

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Notice anything on the photos ?

Yup  looks like ya had a couple of resistors removed ! 

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Guest Jennifer
20 minutes ago, mungass said:

Notice anything on the photos ?

Yup  looks like ya had a couple of resistors removed ! 

They're not actually resistors but it's an easy mistake to make, notice that the stripes are all the same color, not different per a resistor color code/chart. These are MOV's (Metal Oxide Veristors" and for the repair in question, were being replaced by 1N4148 diodes.:smile:

And the reason I fixed it was because take off VANOS boards range from $2,300 per side (the engine has two, one per bank) up to $2,700.

http://www.ebay.com/itm/Genuine-BMW-E39-E52-M5-Z8-Solenoid-for-Vanos-Unit-NEW-11367831450-/122159471884?epid=1122097616&hash=item1c71459d0c:g:~BgAAOSwZJBX~-Fw&vxp=mtr

http://www.ebay.com/itm/BMW-E39-E52-M5-Z8-Solenoid-for-Vanos-Unit-Genuine-Brand-New-11-36-7-831-450-/361183151555?epid=1122097616&hash=item54183185c3:g:KOYAAOSwxYxUs8~7&vxp=mtr

 

Jen

Screen Shot 2017-08-08 at 4.26.41 PM.jpg

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  Yup Jen do notice , a lot more obvious on the pc compared to the 8x4 tablet , and why wouldn,t you .

Many moons ago when I was learning the poker machine repair trade or slot machines as you call them over there , I was with a small private business , and we repaired every board we could , money was money , and a jumper wire didn,t cost more than a couple of beers  unlike the Aristocrat board jockeys who were our competition ,  rip it ,  swap it ,  send it back to factory when box was full . ha ha 

was checkin a couple of curley chords off the 3500 a few weeks ago that didn,t  work , checked continuity and both had none at same pin , took a punt and  cut 3 inches off the most stretched end    and   bingo  problem solved , resoldered ends and when wires of offcut  were stripped back just for interest ,  both white wires in the leads  had breaks   :blink:   ,mmmm  go figure , :cool:

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Guest Jennifer
On 8/6/2017 at 10:42 AM, Jennifer said:

It would be interesting to see this compared to a CTX3030.

Jen

Ask and ye shall recieve, inside a 3030 for comparison (he's re attaching his GPS module).

Jen

 

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Jen, thanks for the cool videos and thoughtful posts in this thread and the forum.

All, on the subject of "good design" or "poor design" to directly solder wires through thru holes I opine this is not a black and white true or false issue.   I started the first 13 years of my electrical engineering career designing airborne electronics for the USA (and friends') Dept of Defense.  In this environment, such a termination was forbidden.  (I recall faintly that waiver could be had, however if the circumstances denied any other type of connection and the soldered wire received additional strain relief than just the soldered connection.)

Having said that, in many years of industrial and consumer design there are always cost, performance, size, reliability, ... tradeoffs.  The inherent reliability weakness of this termination can be mitigated as Jen noted above if other mechanical aspects of the design prevent the wire at the PCB interface from moving under the duress of shock and vibration.   

So, are the BMW and Zed "poorly designed" because they don't meet the standards of Mil-Std 810?   No, not necessarily given cost, size, manufacturability ... constraints.  As Steve notes on product evolution, if ML has seen a noteworthy failure rate due to the design of this termination, then YES.  Else, NO.   

 

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