Recently, I acquired a Newton MP 130 with a audio hack in which a headphone jack was ported to the outside. I played with it in this configuration for a while and decided I did not like it. Using the take-apart guide from PDA-Soft.com, I went inside.
Incidentally, this is a cool Newton site if you have never been there and are not afraid to dig in.
Once inside, I could see what was done. The wires from the mobo to the internal speaker were removed and the line from the external jack were soldered onto the pads for the speaker on the mobo. After sizing up the situation and making note things, I decided to undo the mod. Not having a soldering iron with me (as all my tools were back home and I in Atlanta at the time), I picked up a ColdHeat soldering iron. You have all seen the commercial onTV about the battery powered soldering tool that is also cool to the touch sconds after use.
The end was a bit blunt, but would have been fine for what I needed to do given my comfort with soldering and the size of the pieces I would be working on. Now something to make note of, the ColdHeat has a split tip and heats the solder to a melting point by passing a voltage through the split tip when it is shorted out by touching the solder or parts to be joined. I was able to easily remove the wires, but I found it to be a bit challenging to add new wires to the board for the speaker. This was due, in part, to the angle I had to hold the iron at to make the short to generate the heat. I rapidly became bothered at the fact that the tip was not electrically isolated as one would find in a much nicer iron, but I carried on. I found that one problem I was running into was that I really needed some good flux, yet had none. This may have been part of the problem, but the longer I worked at it, the more rapidly things began to deteriorate.
Long story short, I lifted one of the pads I was working on clean off the darn board. I also noted that the tip does indeed retain heat the longer it is used, both from prolonged use and from long periods of time of actually soldering. I also noted that the batteries were generating a bit of heat and the iron was becoming quite warm in my hand. At this point, I called it a night and took the batteries out. They were much warmer that I cared for.
The next day, I took it back and got a Weller for a little less with a fine point tip (like a super sharp #2 pencil) and some good flux paste. I was able to anchor my wire to the trace leading up to the now missing pad and finish my job without a problem. The MP also seemed to suffer no ill effects from the manner in which the ColdHeat (electrically) generated its heat.
Bottom line: was the ColdHeat a bad iron? No, it just was not the right tool for the job I choose to apply it in.
If I was still working on stereo components, I would probably keep one for quick and dirty jobs. Since most of what I do now is significantly more precise in detail, I do not think I would try to use one again, especially now knowing that it passes a current through the end of the tip (I never really thought about it when I bought it although I think I casually was aware of this fact). I also would limit my usage of it to situations where I was concerned about using it extensively (meaning I have thirty or so joints to make and the tip will be hot for a noteable length of time) as this leaves residual heat in the tip making it not so cool to the touch (but not hot enough to burn) and the batteries would get hot. It works as advertised, but I would not reccomend it for projects and hacks if you are needing to work on tiny stuff. Had I used flux the first time, I might have had a better result.
Don't flame me to hard as I know there will be some out there with the "Duh! I could have told you that" responses, but I firgured I would give it a shot since I wanted to own one anyways. My decision to not keep it was purely financial in nature and in consideration that I could see my personal usage of this type of iron would be less than I originally thought.
So if anyone out there is thinking about buying one, I hope this helps you pick the right tool for your specific job and illuminates whether you can benefit from this type of iron for that job.