Solder joints breaking lose

[Darin]

I have the SM Pro 3 detector that came assembled. I am having trouble with the solder joints at R10 trimmer coming lose. I have soldered them 4 times cleaned the board with alcohol and old tooth brush but they breaking lose. Is there something else I can try to get the solder to stick to the board ?

Thanks for any help

Darin

[ODM]

Sounds like a cold solder joint or lack of flux. You need to re-do the solder joints completely. Wick away the solder, then clean the board, and finally do the soldering again. With most solder wire, the flux is inside the wire and will boil off in a few seconds. If the joint is re-flowed after that, it won't stick to much anything any longer and will have a dull cracked surface. If the parts were too cold it didn't flow properly on one or either of them which will leave the solder joint brittle.

* be sure to have a clean solder iron tip, wipe it clean once it's hot and apply a bit of fresh solder wire
* heat up both contacts with iron tip before applying solder (about a second) to make it flow and adhere
* add enough solder to wet the pad and component leg, it should have a tent like shape instead of a ball like shape, and flow to the edges of the pad and up the component leg
* don't move or shake the joint right after soldering, let it cool on its own

Some trimmers come with storage grease on them or non tinned legs. It's a good idea to pre-tin parts that don't have a bright shiny look on them, or that are hard to solder.

[Funfinder]

4 times? Perhaps you have destroyed (overheated) already some electronic parts with that.
You need superglue and thin copperwires and then solder everything until it sits bombtight.

[ODM]

Please keep superglue away from any solder operation. Adding extra copper will not help a cold or drossy joint. "The road to hell is paved with good intentions" funfinder, please read about how soldering works first!

The parts to be joined need to be clean and only surface tinned. If solder joints are heated without flux, they will form dross and make the joint more brittle.

If proper soldering practice is followed and the joints still fail, most likely the trimmer (potentiometer) is mechanically stressed. If it is a regular adjust consider panel mounting it with multiple strand wires, and heatshrink sleeve on trimmer legs for tension relief, and a tie down on the board next to the solder pads. Caulk is used in the industry for tension relief, as it is fast and reliable, but it is harder to redo compared to tying down wires with cable lacing cord or zipties.

[Koala]

Photo of the problem would help.

[ODM]

Also I don't like making contradictions without providing references, so here

Darin's solder joints might have no problems and the issue might be just mechanical stress, but here's a basic guide on how to do reliable solder joints and more importantly, why it's done the way it is.

WellerSoldering.pdf

[godigit1]

After 4 times soldering and applying a large amount of heat you may have lifted the pads from the board . Especially if its a single sided board. The boards are made either with a epoxy glass or poly emit material, this has gel layer on the surface and between pre-impregnated layers of the glass weave.
The gel coat cannot stand up to too much heat of soldering. Inspect your board under as high as mag as you can usually 10x is enough. If the pads are lifted you will never get them to stick to the board. If the traces are intact the connection to the pot is ok (*Just Floating off the board ) then lock it in with glue. Once you do this you wont be able to de- solder or re-solder without scraping to do so.

In this case my self I would hard wire to the pot from the last trace terminations make sure all connections are good and lock it down with glue as funfinder says. I think he was maybe just too brief with the hows and whys.

[ODM]

Yeah, if there's broken tracks it's a whole different issue. When mounting wires to exposed tracks and such I would suggest a small dab of "garage-brand" epoxy glue (araldite etc) or high-temp hot melt glue as tension relief for the wires. Superglue has no filler in it and therefore doesn't really make for a long term reliable mechanical bond unless between two flat porous surfaces.

[Darin]

Thanks for the help guys,
The pads where pretty much gone at R10 so I hard wired it back to the last trace termination. Adjust R10 to 0 volts at pin 6 of NE5534 and R2 set at 3.07K. That problem fixed.
Found a connection at C11 in about the same shape ( came to me like that ) so I soldered C11 to R28 and that fixed the problem I was having of the coil making a thumping sound when a target was passed at 3" or less.
walked away to get some coins to test and the detection was gone when I came back so first thought was R10 again but the voltage at pin 6 of NE5534 was at 0 volts so I checked R2 adjustment -.027 ( had been set at 3.07K ) if I touch IRF9640 resistance will go back up. Looks like more of the same problem with the way this board was soldered from the start.
I just wonder if anyone has got a good detector from this guy.

Is there anywhere to get a good PCB for the surf pro that is proven to work or do you have to make it yourself ?

Thanks again for all the help guys.

[godigit1]

Looking back at the your first post you say sm pro 3, Did you get the kit from Ebay?
I built the sm pi pro kit from there, I had no problems with the build it was assemble and go. Its down now for a bad on board trimmer. Pretty much what yours did except I was actually adjusting it when it went. Same with one on my hammerhead. I would check that first.

[Darin]

Looking back at the your first post you say sm pro 3, Did you get the kit from Ebay?
I built the sm pi pro kit from there, I had no problems with the build it was assemble and go. Its down now for a bad on board trimmer. Pretty much what yours did except I was actually adjusting it when it went. Same with one on my hammerhead. I would check that first.

Yes, same kit, mine came assembled. It worked fine when I first got it then I turned it off one day and the next time I turned it on I started having trouble with it. NE 5534 went out, R 10 solder joints kept coming lose. lost detection under 3" then found IRF 9640 was losing connection at the pads so I wired it back to the last trace termination.

Just finished it tonight and seems to be working well with my 8" 3DSS round coil ( 330/46 LITZ, 328uH, 1.7 R ) Doesn't really matter to me why I had so many problems with mine because I learned something as I worked on it and fixed it. Now I have two detectors, A SM Pro 3 and the MPP I built.
Thanks to all the help and knowledge this site offers.

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