Something is wrong with my simple solder job?

[pete]

TL;DR Summary

A PTT radio switch extension has gone wrong somehow.

I have a Yaesu VX-6 Radio. Perfect for my needs but I need a hands free PTT kit. Very difficult to find but I hunted about and finally found a US-based company that had hands free kits made up to order in China and I bought one of their kits.
When it arrived I plugged it all in and it worked, the PTT worked exactly as it should. I've been searching for a working one for the last year or so and have been through several radios and even more PTT hands-free kits.The one problem with this new working kit was that the wire from the splitter to the PTT was about 10cm long, so too short to hold in my hands. Meaning I would have to take my hands off the controls to push the PTT. This defeats the whole purpose for me.

So I thought no problem. I'll cut the wire and I'll solder on an extension with a little 3.5mm jack plug and socket. I did this and the PTT did not work.
I undid it, carefully cleaned all the wires soldered the 4 splices again. It still did not work.

I reconnected the PTT button without the extension to check it was not damaged somehow using some little connector blocks and it worked fine.

I questioned the extension with the plug so I got the multimeter out and checked my extension it, worked fine.

I questioned my soldering, this wire is very fine, about .4 mm and coated so I soldered a test part with spear wire and checked with the multimeter, all good, checking also for shorts between the two cores.

I soldered the extension back onto the hand's free kit and checked all the connections solder to solder both to be sure they were good and to make sure there was no short between the two tiny cores. All fine but still the PTT would not transmit.

After soldering, undoing and redoing this half a dozen times I've come to realize there is something going on here I don't understand.

I'm banging my head against the wall here, I don't know how much time and money I've spent over the past few years trying to find a hands free kit and I'm really close here.

If anyone has any idea what's going on with this VX-6 kit and why the extension will not work I'd really appreciate some advice.

PS there is some unusual wiring in the PTT that I don't fully understand, I'll provide a schematic from Yaesu.

 

[tech99]

I think maybe you have used a jack socket with an in-built shorting switch.

 

[Tom.G]

Coil-cord is extremely difficult to solder; so much so that crimp connections are often used.

There are two reasons for this:
1) Upon close inspection you will note that the conductors in the coil cord are wrapped around what looks like thread. That would be bad enough as the thread would decompose at soldering temperature. Usually the thread is a synthetic though, a plastic of some sort. At soldering temperature it melts and decomposes, thereby contaminanting the solder joint.

2) The conductor in a coil-cord is not plain Copper; Copper hardens, turns brittle, and breaks with constant flexing. So Phosphor Bronze is often used for the conductors. Phosphor Bronze is springy and withstands the flexing rather well. However some Phosphor Bronze alloys, in my experience, are also difficult to solder; solder just doesn't stick to them. (That could be contanimation from the threads though, it's been a long time since I've tried.)

This does not rule out the suggestion by @tech99, above, that the wrong jack could also be a problem.

Cheers,
Tom

/edit:
Also make sure there is good strain relief at any joints you have. Any movement of the wires at the joints will cause a stress concentration at the joint leading to failure. The you have to repair it again.
/edit:

 

[pete]

I think maybe you have used a jack socket with an in-built shorting switch.

Thanks for taking the time. I'm struggling on with this today. I don't know how I would check if it's a shorting switch/jack on the connection, it is an audio cable extension through only a 3.5 mm one. How would I check to see if it is?

 

[pete]

Coil-cord is extremely difficult to solder; so much so that crimp connections are often used.

There are two reasons for this:
1) Upon close inspection you will note that the conductors in the coil cord are wrapped around what looks like thread. That would be bad enough as the thread would decompose at soldering temperature. Usually the thread is a synthetic though, a plastic of some sort. At soldering temperature it melts and decomposes, thereby contaminanting the solder joint.

2) The conductor in a coil-cord is not plain Copper; Copper hardens, turns brittle, and breaks with constant flexing. So Phosphor Bronze is often used for the conductors. Phosphor Bronze is springy and withstands the flexing rather well. However some Phosphor Bronze alloys, in my experience, are also difficult to solder; solder just doesn't stick to them. (That could be contanimation from the threads though, it's been a long time since I've tried.)

This does not rule out the suggestion by @tech99, above, that the wrong jack could also be a problem.

Cheers,
Tom

/edit:
Also make sure there is good strain relief at any joints you have. Any movement of the wires at the joints will cause a stress concentration at the joint leading to failure. The you have to repair it again.
/edit:

Thanks for taking the time to help with this. I'm back at it today. The wire from the PTT attachment on the hands-free kit is 2mm with two tiny cores, about 0.4 mm, one red and one copper coloured. I've got bits of other cables like this that I've salvaged mostly from old audio kit like headphones.

These wires all have three cores, red, green and copper. The wires have some kind of insulation so I try to burn it off before starting the splice. I hold a lighter to the end of the wire and it burns for a moment then goes out, stripping the colour off that section.

The wire on the hands-free kit and the other ones I have don't have a bundle of synthetic cord between them, I know what you mean I've seen it before on other wires. It is there on these too, under magnification I can see synthetic fibres mixed up in the soldered joints. Each core has this synthetic cord in the middle and the copper is wound around it. To prevent pinching I guess.

If it is copper. I wind the splice together then heat and run solder through the joint but as you say very little is staying in there. enough to fix it in place but barely. I'll look into the crimp idea today. There must be a way to splice these together.

 

[Tom.G]

If you have the patience, you can unwind the the Copper from the fibers then cut off the fibers. From a practical standpoint, it is sometimes easier to unwind the fibers from the Copper. Separate them at the end then unwind whichever is more convenient.

The approach of burning off the insulation or fibers contaminates the surface of the Copper so solder will not stick to it; cut the stuff off instead. The Copper should be shiny; if it isn't then gently scrape it clean with a knife blade (or a fine wire brush or fine sandpaper). If you are in the US, it should look just slightly darker than a brand new penny.

If you think you need a little more practice soldering, try to purchase some wire used for house wiring; the stuff that connects the wall outlets and lights. You probably only need 1ft (30cm) because it contains 2 or 3 conductors. Cut some insulation off an end and try soldering it.

The next step would be to solder some 'Lamp Cord.' That is the 2 (or3)-conductor stuff used on plug-in appliances. It is stranded wire and is slightly tricky to get a good joint, you have to get all the strands (even those in the middle) to soldering temperature.

Her is a site that has several tips (and links) about soldering:
https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems

Hope this helps!

Cheers,
Tom

 

[pete]

If you have the patience, you can unwind the the Copper from the fibers then cut off the fibers. From a practical standpoint, it is sometimes easier to unwind the fibers from the Copper. Separate them at the end then unwind whichever is more convenient.

The approach of burning off the insulation or fibers contaminates the surface of the Copper so solder will not stick to it; cut the stuff off instead. The Copper should be shiny; if it isn't then gently scrape it clean with a knife blade (or a fine wire brush or fine sandpaper). If you are in the US, it should look just slightly darker than a brand new penny.

If you think you need a little more practice soldering, try to purchase some wire used for house wiring; the stuff that connects the wall outlets and lights. You probably only need 1ft (30cm) because it contains 2 or 3 conductors. Cut some insulation off an end and try soldering it.

The next step would be to solder some 'Lamp Cord.' That is the 2 (or3)-conductor stuff used on plug-in appliances. It is stranded wire and is slightly tricky to get a good joint, you have to get all the strands (even those in the middle) to soldering temperature.

Her is a site that has several tips (and links) about soldering:
https://learn.adafruit.com/adafruit-guide-excellent-soldering/common-problems

Hope this helps!

Cheers,
Tom

It did help

 

[pete]

Success, after two days of struggling I worked it out with help from you guys, in particular Tom in the last post pointed out that burning the wires was coating them in a residue that made it harder for the solder to stick. This and his advice to separate and remove the synthetic fibres sent me down the road that solved the issue
I can solder, I'm no pro but I've not been not failing for want of skill, though I've not soldered anything this fine before.
I unwound each core and separated the synthetic fibres as advised then cut them away. Each core is made of a dozen or so individual strands of copper and each strand is coated, these stands are thinner than a hair so mechanically removing the coating would not be practical.

I spliced two cores together winding the wires around each other with the coating still on.
Then I balanced a drop of molten solder on the end of my iron and held the iron so the splice was suspended in the drop of solder. After a few seconds, the wires heated to a point where the coating melted away and the solder instantly wicked into the joint. I then immediately removed the solder drop. If I held it there a second too long the solder wicks back out into the drop. I had to practice a bit to get it right.
The black cable shown is 2mm in diameter and the splice less than half a mil.

In this picture with magnification, you can see how the coating has melted and pulled back on either side.

I have a box of Lav mics and wireless audio recording equipment that needs attention and I'm pretty sure it's the same kind of wire. Thanks to all for the advice. Hopefully, this will help if anyone else with the same problem stumbles upon it.