Riders,raYzerman wrote: as I pressed on the LED, it works! Surface mounted LED rectangular (SMD)... will require delicate re-solder by somebody with experience and good eyes, or replace the module.
Lots of people say that soldering is tricky, but if they dumped their poor old tools on me, I'd have a hard time myself. In my job as an aircraft electronics tech, everybody on my team would say they could give an appendectomy to a termite.
None of us had super-powers, but we did have the right tooling.The average would be somebody thinking that rosin was actually good flux, or that acid flux was okay for use on electronics. Flux means FLOW, and you want your solder to flow like water on your connections. Acid flux is for plumbing, if even that. Acid flux will destroy electronics, unless you clean it up with baking soda and water after the work. Rosin flux is lame; it does not work on many metals, and it needs alcohol or a good solvent (safe for electronics) to wash away the flux after the job is done. Forget that old stuff; this is not the 1950s anymore. The best commonly available flux that I know is LA-CO flux, costing about US$ 3.50 for 2 oz. (113 g). This little jar will last you a long time. LA-CO flux washes away with plain water, and it is safe for drinking water pipes.
https://markal.com/collections/solderin ... 4786921519
These same folks might have a soldering iron that is suitable for building power plants, maybe with a "tip" half an inch (14 mm) across. Bogus. You need a temperature-controllable soldering iron in the range of 75 Watts, and a damp sponge to wipe the tip clean and shiny each time before you touch the soldering iron to the work. A small chisel tip (1/8" or 3 mm wide) is a good choice, at the business end. Crank up the tip temperature just enough for good progress on the work, but not so high that the tip gets "dirty" (oxidized) too fast. Just one example here:
https://www.amazon.com/Soldering-Statio ... 0CDNWLJWJ/
Now okay, there are a few things to know. Leaving flux on the board after soldering is a recipe for a quick failure, even if the gear will operate at the time when you are done. Cut down the bristles of an acid brush to get short firm brush bristles, and use it with the correct solvent (usually alcohol) and toilet paper to clean away all flux when you are finished. Old flux will collect dirt and contaminnts, and may damage the printed circuitry.
63-37 solder (lead/tin, by percentages) melts faster than the others. 60-40 solder is the most common old-style solder, but it is getting rare. I recommend lead-free solder, unless you have a vented work table to draw off the lead-laced fumes.
It's a good idea to remove all of the old solder from a job, before installing new parts. For that, you need Soder-Wick, or some similar copper braid with flux. Lay the braid on the old solder, apply the soldering iron, and the hot copper braid will absorb the old solder like magic. Add flux if needed, for good results. Copper braid goes for maybe US$ 1.00 per foot (30 cm), but you can pay much more. There is no great benefit from any extra expense, for copper braid.
Eyeglasses? Yeah, I have them, but perfect vision is not needed. What IS needed for fine electronics work is a low-power microscope, preferably the binocular type. The one-eyed microscope that you had as a kid is just too powerful. You need maybe 15 X power, +/- five X or ten X, and NOT what a microbiologist would use. You can find them in the thrift stores, or on websites like eBay and Craigslist. You will be amazed at how well you can do micro-soldering with this good tool.
Practice definitely helps. Make up some repair jobs on old junk electronic parts, and sharpen your skills. You can be a soldering ace in a matter of days. When the job is done, your soldering should look like new silver. Dirty, gray, granular soldering is sub-standard. A clean iron, good flux, and new solder are the ingredients for reliable repair.
