Soldering queries

[Jonathan Wilcox]

Hi guys,

I’m new to the forum and don’t know much but hopefully in time I’ll be able to repay you with knowledge.

I encountered a few wondering issues when repairing my technic 1210 turntable today.

Why do the little pads lift up when you apply heat for too long on a circuit board? Is this fixable?

Why do I get specs of black in my solder? Even though I am cleaning the tip and using rosin flux?

Is it ok to dip your tip in the flux pot to de-oxidise it - or is it bad that the oxidisation remains floating round in the rest of the flux for future use?

What is the oil residue that seeps out of a connection / pad when soldering a joint?

Is flux only used on oxidised joints? Or should it be applied when soldering fresh wires too?

I have a small hum afternoon internally grounding the wires - the signal from the right side is stronger than the left too. What would be the issue here?

Finally a very strange question - is it ok to drink out of a cup that has once had rosin flux in it?

Thanks so much,

Jonathan

 

[Audioguru]

A cheap soldering iron does not have a controlled temperature. To turn on fast and allow you to make many solder joints one after the other then its power is too high which causes it to get hotter and hotter if it is sitting doing nothing. Then the pads on a pcb lift, the tip wears out soon and the rosin in solder is incinerated before it cleans the pad and wire. My Weller soldering iron is about 50 years old and is still made today the same as before. It keeps the tip always at the correct soldering temperature, its tip lasts for many years and the solder works perfectly. It has a lot of power when needed but can sit all day without overheating.

Most people use rosin cored solder that has the rosin flux inside it. Rosin has chemicals in it to help clean the pad and wire so I would not drink from a cup that had rosin in it.

 

[(*steve*)]

Hi guys,

I’m new to the forum and don’t know much but hopefully in time I’ll be able to repay you with knowledge.

I encountered a few wondering issues when repairing my technic 1210 turntable today.

Hi Jonathan. Welcome to Electronics Point.

If we can help fix your problem, that (weirdly enough) is payment enough for most of us.

Why do the little pads lift up when you apply heat for too long on a circuit board?

Generally speaking this is caused by too much heat applied for too long. Some older (and even some not-so-old) boards are highly subject to this because the glue holding the copper to the board is poor.

This is usually caused by a soldering iron that is too hot left on for too long, but it can also happen if the soldering iron is not hot enough or can't supply heat fast enough and takes a very long time to melt the solder.

Another cause is stress on the board, but this normally doesn't happen while soldering.

Is this fixable?

It normally is, and with older equipment it's a lot easier to fix. Generally you'll run a wire in place of the torn track or missing pad.

However it's vital that you have solved the issue of why it happened in the first place or you just might make the problem worse and worse.

Why do I get specs of black in my solder? Even though I am cleaning the tip and using rosin flux?

It's typically residue of burnt flux or other gunk on the board or in the joint. If you've touched a wire and melted some insulation, this can cause it too.

Is it ok to dip your tip in the flux pot to de-oxidise it - or is it bad that the oxidisation remains floating round in the rest of the flux for future use?

I wouldn't. It's better to use a damp sponge or a ball of brass swarf (these days it's more likely to be yellow coloured steel). I prefer the latter. You just poke your iron's tip into it a few times to clean it up.

What is the oil residue that seeps out of a connection / pad when soldering a joint?

If it's the sort of "wet looking" residue around a completed joint, that's flux. Depending on the flux, you can leave it, or clean it with water, alcohol, or special board cleaning solvents.

Is flux only used on oxidised joints? Or should it be applied when soldering fresh wires too?

You should be using solder that has its own flux in it. It gets used on every joint that way. Additional flux is only used rarely, either with heavily corroded leads, or possibly when you are re-flowing existing solder.

For the best joints and easiest soldering experience you should clean wires and pads before you solder them. In practice this wastes more time, and you don't usually do it unless there is a specific need.

I have a small hum afternoon internally grounding the wires - the signal from the right side is stronger than the left too. What would be the issue here?

You'll have to give us more information. Did this happen after you performed repairs? do you have a schematic? Do you have pictures? How old is the equipment (and is it valve or transistor)?

Finally a very strange question - is it ok to drink out of a cup that has once had rosin flux in it?

I certainly wouldn't. Cups are cheap.