What is a "cold solder joint"

[re510]

The reason i'm asking is that i have a mid 90's 5-ch carver and the front right channel has a very slight static buzz sound but only on this channel i did some trial and error and discovered is is the amp and it is only that channel. So my question is what sound does a cold solder usually yield? and can you identify it by looking at the solder joint? and do you have to remove the old solder or just re-heat and apply new. thanks

[dragon1952]

A cold solder joint is typically a joint where maybe the soldering iron wasn't hot enough or enough heat wasn't applied for the solder to melt and really form a good bond. Or maybe the surface being soldered wasn't nice and clean and contaminent free. You may need a magnifying glass but usually you can wiggle the joint and notice a 'crack' in the solder joint. Sometimes it is very noticeable and sometimes they are hard to find. But they can cause static noises and/or intermittant cutouts, etc. It is best to suck the old solder out, clean really well then resolder although you can sometimes just remelt the existing solder or add a little new and get away with it but the problem will sometimes return.
It's hard to say if that's what you've got. They tend to be a little more intermittant unless it's a really bad joint.
It may be more likely to be something like a capacitor or a transformer? I don't know.....I'm not an electronics expert. I just know a little about soldering and finding solder related problems.

[heiney9]

Originally posted by re510
The reason i'm asking is that i have a mid 90's 5-ch carver and the front right channel has a very slight static buzz sound but only on this channel i did some trial and error and discovered is is the amp and it is only that channel. So my question is what sound does a cold solder usually yield? and can you identify it by looking at the solder joint? and do you have to remove the old solder or just re-heat and apply new. thanks

Taking a stab from my electronics class days. It's basically when the heat applied to the solder isn't enough for it to flow properly. Solder has flux in it which makes it "flow over" the solder joint to join the two surfaces. It needs to reach a certain temp range to properly bond the two surfaces. Usually, NOT always you can see a cold solder joint because it tends to look "duller" or pale in comparison to a reg solder joint which tends to be shiney. However with most older equipment the solder has lost it's shine.

Please other correct me if this is incorrect.

H9

[bknauss]

Both answers are correct... good job :)

When the parts/solder pads the solder is "connecting" to aren't warmed up enough, the solder doesn't properly bond to the surfaces. You can also get a cold solder joint if you jiggle around the parts you're soldering while the solder is cooling down. You get a bad connection, so the resistance between the parts shoots up, and it doesn't take too much to kill the connection and at least make it intermitent (did I spell that correctly), or even break it apart.

[Roy Munson]

I had this problem with my guitar amp [Fender Blues Deville] a couple of years ago. It would cut out intermittently and I couldn't figure it out so I took it to a tech and he said it had cold solder joints. He fixed it by redoing most of the joints and I haven't had a problem with it since. Until then I had never heard of such a thing as cold solder joints. The tech explained it to me the same way that it has been described here.

[BobMcG]

I've seen a lot of cold solder joints and the guys making them don't even realize they're doing it because no one showed them how to solder properly.

My line of work deals a lot with multiple strand wires using a horizontal twisting of the wires to mate them. The proper way to solder them together is to apply heat to the wires from the bottom until they are so hot that when you touch the solder to the top of the wire it "seaps" right down into and through every strand and pore of the wires. It's the wire that melts the solder, not the soldering iron or gun tip. The solder joint is very complete, strong and shiney.
In a cold solder situation the soldering tip is placed against the top of the wires and solder is touched to the hot tip, melting the solder down and over the wires. The wires are connected but in a very poor manner. Its not complete, not really strong and dull in appearance.

It takes more time and patients to do a hot solder joint than a cold one but it's a far superior solder joint.