Troubleshooting a soldering gun

[sbmathias]

I have a "classic" soldering gun that barely gets hot. Inside, there isn't much to go wrong, it seems. A 2-speed trigger switch, a big coil of fine wire that goes through a coiled sheet steel cylinder, and a light bulb.
How can I troubleshoot this? The light bulb lights up, and I have cleaned the contacts of the tip. Voltage across the tip is only about .3VAC, but I have no idea if that is good or bad.

[Pherdie]

I assume you have the type where the interchangeable tip is fixed to the gun with two nuts??? If so, try loosening and then re-tightening the the two nuts.

I always encountered the same issue with the guns and that always worked for me.

[Shaidorsai]

It's pretty simple. The switch is in series with the primary of a big step down transformer across the power mains. The primary of the transformer is made up of many turns of small diameter wire. The secondary of the transformer is made up of just a few turns of very heavy wire leading out to the soldering tip. The high voltage primary draws a small current which is transformed by induction into a low voltage at a high current . The soldering tip is the electrical load that makes everything run in balance. If it has a relatively low resistance, heavy current flows and the tip gets hot. If the tip's resistance is relatively high, on the other hand, only a small current flows and the tip does not get hot enough. Several things can cause the tip resistance to be too high. Loose or corroded conection of the replaceable tip to the iron has already been mentioned. Gotta be tight and clean here. If the tip itself is worn, broken, or nearly so, it effectively becomes a thinner wire, unable to conduct enough electrons to permit a heavy enough current to flow. If yours is as old as mine is, do yourself a favor, and replace the copper tip. They are cheap, and available at most radio shack stores. Should perk it right up.

[darryl]

If you have about .3 vac at the terminals, it's working fine. As others have said it's all about the connections. Many of them these days have a cheesy way of attaching the tip, and they don't really get good low resistance contact. That really is the key to the whole thing.

Does it have aluminum terminals- what a nightmare that is.

[Stepside]

Tip Shape

If the tip is a large curve it will not get hot. So if the tip is old and does not have the original shape, either replace or reshape. I have made extended tips up to 18 inches long for special jobs. Use #12 copper wire and make sure to get a tight bend where you want the heat point to be. Also flatten it a bit and shape it to match a new tip. Also check the connections where the tip meets the gun as dirt/loose connections will affect performance.

[Paul Alciatore]

I guess others have answered but here's mine.

If the light comes on, the primary coil is OK. The secondary coil is one turn and so massive it would have to be sawed in two to fail so it is probably not a problem.

The tips for these guns are bare copper and tend to be eaten away by the heat and solder. I believe the copper is actually slowly disolved into the solder. They also can build up corrosion at the connection points. So one or both of two things are usually sufficient to get them back in action. The first is to loosen and retighten the nuts as said above. The second is to replace the tip if it has a thin area near the tip. The thin area will be a higher resistance and will prevent full current from flowing, thus lowering the heat output.

Of course the tip must be properly cleaned and tinned to transfer heat well. Clean with a fine wire brush and immediately tin with solder and flux.

A tip: the tips can be fabricated from 12 gauge, solid, bare copper wire. Just use a scrap of electrical wire, strip it and bend it into shape. Don't worry about the fancy tip shape the factory ones have, just bend it into a small radius half loop. These home made tips actually last longer than the factory ones and work 90% as well. And they are a lot cheaper and easier to find on a Sunday night.

[sbmathias]

Thanks!

Thanks to all for the insight and information. After pulling the guts out to inspect them, then reinstalling soas not to lose any parts, it works fine now. Despite my initial meager efforts at cleaning the contact, that must have been the problem all along.

Will have to try the 12-ga wire tip some time.

[timz1999]

keep thew tip cleen

if the tip is dirty it will not heat properly. keep it clean !

[pcarpenter]

As has been previously stated, the nuts that establish the electrical connection have to be good and snug to keep the connection resistance low. Unfortuantely, normal heat and cool cycles seem to be all it takes to loosen these up just a bit.

I have wondered how many of these have been tossed in the trash for a problem that could be fixed with a nutdriver

Paul