Soldering question...

[Dokkodo]

Ive a question about soldering, in case anyones an expert... Im trying to repair some failed electrical joints in some speaker drivers. They have two delicate wires that go into the voice coil under the central dust cap/dome, but they have perished through oxidation i think in damp storage.

I want to solder a new connection to these wires that go into the voice coil, but i cannot for the life of me get any solder to stick. I have gently abraded with a stanley blade, fine sand paper, and heat to try and get rid of any possible coating, to no avail. Using flux and tried a couple of types of bog standard solder with a cheapo soldering iron.
Im stumped. If i can just make a reliable electrical connection (has to withstand being wobbled vigorously at many frequencies) i think i can salvage these drivers and they are decent, full recone kits are laborious and expensive so it would be great to avoid that. So im hoping i just need bettert solder/flux/iron?

 

[Spectric]

You need quality solder and a decent iron with a clean and tined tip. Then tin the wires, small abrasive paper to clean those contacts and tin them. Now you can attach the wires as both sides are pre tined. Are those flat contacts copper or steel, I am wondering because if they need to withstand being wobbled vigorously at many frequencies then copper would probably fatigue and fail so they might be steel. In this case it can be more difficult to solder.

 

[Dokkodo]

Ok but what does quality solder entail... are there different grades or ones especially for trickier applications than just copper to copper? because I can solder copper absolutely no problems with the current stuff i have...

 

[ajs]

Sounds like you've tried most of the usual answers.

Generally the coil will be enameled wire, the textbook answer is to crank up the temperature, I find with my temp controlled iron it'll work if I set it to 400°C or higher. If you have a simpler type without a thermocouple you may need to go to 450 or so. Additional flux (rosin based) is a big help as is 60/40 solder rather than lead free.

The other alternative is to abrade it away, which you've already tried but I would question how effectively - no criticism of you but it's awfully close to a rather delicate diaphragm. In my experience you need to remove the whole lot in the area to be soldered, you can't bank on the solder flowing through odd scratches or cracks made in the enamel.

 

[Dokkodo]

ok i can try abrading more... i got it from yellow to shiny silver though so i thought id be through to bare metal by then.
doing a bit of reading now, it seems silver solder and a hotter iron might help? It might be time to invest in a better soldering iron anyway...

 

[Phil Pascoe]

You won't solder silver solder with an iron.

 

[bourbon]

decent flux

 

[Dokkodo]

ok so decent flux and not an iron... a gas soldering jobby? Ive got one of them but couldnt fill the damn thing up last time i tried

 

[Phil Pascoe]

Find out what you are doing wrongly. There is no reason why you shouldn't solder it perfectly easily with an iron.

 

[Dokkodo]

Indeed, that is exactly what im trying to do, because it isnt soldering easily at all, its solder repellant with all ive tried so far. Ill get some better flux and a hotter iron and see how i go.

 

[sawtooth-9]

Solder relies on metal to metal contact.
When wires "corrode" they form an oxide on the surface and this MUST be removed to provide a suitable base for soldering.
Using an acid to remove the oxides only results in a metal salt on the surface - again, not great for soldering.
Best advice is to replace the wires and start again

 

[Oldman]

Maybe the wires are aluminum, or copper-clad aluminum, the op did say he scrapped back the surface to silver metal.

 

[Fergie 307]

Solder relies on metal to metal contact.
When wires "corrode" they form an oxide on the surface and this MUST be removed to provide a suitable base for soldering.
Using an acid to remove the oxides only results in a metal salt on the surface - again, not great for soldering.
Best advice is to replace the wires and start again

I have often found that plumbing flux overcomes this sort of issue. Seems to be much more powerful. Just smear a tiny blob, maybe a mm round or less on the surface then use your regular iron. I would advise you clean thoroughly afterwards as its powerful stuff and if you leave any residue behind it will eat its way through your delicate wiring.

 

[Johnwa]

Are they copper wires at all, or are they that horrendous fabric stuff impregnated with copper that are spot welded to the connection. If they are copper/fabric forget it, you won't solder it successfully. Having said that it does look as though the wires were previously soldered, in which case it is thoroughly clean the wires and contacts, use 60/40 solder, use a hot iron and if you can, use flux to clean everything. If that doesnt work get new speakers. Sorry

 

[imageel]

I have an electronics background, if I mention Marconi you'll get an idea of age.... -indeed as others have stated wires are likely enamel coated and you do need to maintain a high temperature and for a considerable length of time before the coating will bubble off.
It looks to me that you could easily draw a scalpel or similarly sharp blade across the exposed contacts and then get the wire to tin properly

 

[Fergie 307]

On car wiring, generally with crimps, you tend to find that even when you strip back the wire is often badly tarnished and consequently a pig to solder. I have found the plumbing solder paste works every time in these cases. Definitely worth a try. And a nice hot iron!

 

[imageel]

Forgot to mention, assuming you successfully achieve a sound soldered joint, I'd coat the loose wires with a small amount of epoxy glue so that it is mechanically affixed to the cone itself. That way you minimise the strain on the joint in pretty much the same way the original manufacturer did - the two black blobs..

 

[John Brown]

Look on line for a no-clean flux pen. I think plumbing flux might be too corrosive.

 

[Spectric]

Avoid lead free solder, a quality solder will have a silver content. Multi core 362 is a good general purpose solder and 366 for those more troublesome jobs. Both use rosin flux.

 

[Dokkodo]

Thanks everyone! Have ordered a nice new iron and ive got some plumbing flux now and will give all these things a go and report back.