Soldering - inability to avoid cold joints

[KrisZ]

Did you wet the tip of the solder gun? If the solder melts and coats the tip, then it’s hot enough.

Generally speaking you need to heat up the connector, not the wire. While heating, periodically test with the solder wire, if the temp is in the correct range, the solder will melt and flow like liquid.

 

[SOUNDMAN5000]

Practice makes perfect OP, Keep trying. I'm no expert but I do solder AV wiring from time to time. I use silver content solder from WBT I buy from Parts Express, Its melts at a very low temp but expensive. I never needed a gun but I do always need new fresh tips for the iron.
Perhaps find a buddy who solders often and let him have a go at it?

 

[SumGuy]

Apply a drop of nitric or phosphoric acid to the surface, and then touch it with the iron and fresh solder at the same time. The solder will flow right over it like butter. I use this technique to solder fine stainless steel wire (36 guage stranded). There will be a puff of smoke from the acid burning away and it will be nasty for a second, but it's worth it.

 

[Touring5]

If I were still doing much electronic work, I'd buy a nice Hakko station. When they were new in America back in the early 90's, they were a steal - better than Weller (IMO) at a much lower price. Now they're priced commensurate with their quality $$$.

 

[Towncivilian]

I bought a digital soldering station. Sure, made in China, so, not super expensive, but it works really well. Better than a soldering iron ever did.

This one.

YIHUA 939D+ Digital Soldering Station, 75W Equivalent with Precision Heat Control (392°F to 896°F) and Built-in Transformer. ESD Safe, Lead Free with °C/°F display (Black) https://a.co/d/03PnWUBz

I bought a similar GEEBOON station. Very impressive for the price. Far better than my experiences with a soldering gun which is unwieldly and feels more like a sledgehammer in comparison.

 

[STL_G8GT]

GEEBOON TC22 soldering station... https://www.amazon.com/dp/B0FC6GX9CC?ref=ppx_pop_mob_ap_share

Bought this to replace a weller iron. It's freaking AWESOME.

But to OP, it's pretty clear that the vice is pulling heat away from the fitting. You need to hold the wire further down.

 

[Towncivilian]

GEEBOON TC22 soldering station... https://www.amazon.com/dp/B0FC6GX9CC?ref=ppx_pop_mob_ap_share

Bought this to replace a weller iron. It's freaking AWESOME.

But to OP, it's pretty clear that the vice is pulling heat away from the fitting. You need to hold the wire further down.

Yeah, that's the one I've got. Super pleased with it. I would like to get a hot air rework station at some point too.

 

[JHZR2]

When I needed more heat, I use a Weller soldering gun. I never had an issue soldering anything where I couldn't get the solder to flow between the strands of wire and whatever I was soldering to. Been doing it for over 45 years now.

Precisely why I’m saying it is a learning curve and I still haven’t learned properly.

Sure, maybe your gun is “hotter” than mine. But 140W is a lot of power I’d think.

Soldering is pretty easy and a joint like that shouldn't be an issue even with a cheap iron. A video of what you are doing would help. If I was doing it I would clean the tip of the iron with a wire brush, dip it in flux, tin the end of the iron, dab a little paste on the wire and joint then solder the pieces together. It's not rocket science.

That’s essentially what I did.

Heat the gun to melt the old solder, remove as much as I can. Clean the tip with an abrasive. Melt new solder on tip.

Get flux on work. Touch tinned tip to work. Touch solder to opposite side where I want it to flow from.

And I get what I get.

Did you wet the tip of the solder gun? If the solder melts and coats the tip, then it’s hot enough.

Generally speaking you need to heat up the connector, not the wire. While heating, periodically test with the solder wire, if the temp is in the correct range, the solder will melt and flow like liquid.

Yes. But it was far from being hot enough. Put it on the wires and all heat is sucked away and I got
What I got, even after sitting the wetted tip on there for over a minute. Minutes perhaps in hindsight.

 

[TooManyWheels]

Clean the tip with an abrasive. Melt new solder on tip.

Get flux on work. Touch tinned tip to work. Touch solder to opposite side where I want it to flow from.

My personal approach has always been to dip the solder in the flux just enough for a thin coating, then use this to tin the tip and also to do the joint. I never apply flux to the joint.

I wonder about your "opposite side" approach. This sounds like torch soldering, where you want the solder to come from the cold (relatively speaking) side to the hotter side. In a situation like yours, with a hard to heat component, you heat that side first, and get solder onto it as soon as it will melt. Then the solder itself helps provide heat transfer between the gun/iron and the other components.