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I'm visually inspecting a bike light that does not work properly anymore after some years.

Do you have any idea of what's the "dirt" in the photos?

Is that cause of concern? Is it just rework during assembly or a component failure...?

The rest of the lamp looks fine, the light is waterproof and no sign of water leaks found.

What are those BSSAA components?

pcb photo 1

pcb photo 2

pcb photo 3

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    \$\begingroup\$ Green stuff looks like corrosion local to the BSSAA components. Looks like something has leaked, melted or sat in a puddle of water. Try cleaning that area up with a stiff brush to see what the damage is underneath. \$\endgroup\$
    – mhaselup
    Dec 25, 2020 at 1:43
  • \$\begingroup\$ The components would appear to be transistors, based on the 'Q3" that appears to designate one of them, though the legend seems a bit vague on the other (and several other components seem to be undesignated as well). What transistor? I can't find a match for that marking, so no idea. \$\endgroup\$
    – Ecnerwal
    Dec 25, 2020 at 4:24
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    \$\begingroup\$ Corrosion, aided by elctrolysis, where water got in. (It's a bike light. Water got in. Possibly salt water, in winter) I've seen a more extreme case dissolve PCB tracks, in a weather station subject to sea spray. \$\endgroup\$
    – user16324
    Dec 25, 2020 at 12:25
  • \$\begingroup\$ Thank you all for your helpful answers and comments! I don't know how water entered the light, which is branded, high quality, robust, 200 USD, 1 meter waterproof and got in touch with only rain and snow and maybe some salty water sprays from the road. Anyway I'll try to fix it. \$\endgroup\$
    – haku15
    Dec 25, 2020 at 15:43

3 Answers 3

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Ah, flood damage! (That keeps happening in our department.)

That crust is what happens when a big droplet of water sits on some power-supply pins: electrolysis destroys the metal, also making gas bubbles, until the water fills with conductive salts, then the heat from high current vaporizes the water and halts the process. It looks like your water-blob sat between the two chips, also getting underneath both. Even inside a plastic enclosure, condensed water from cold conditions can collect to form one big droplet.

Don't be surprised if some copper traces, (and even IC pins) are completely etched away. Beware: the corrosion might be full of heavy-metal salts from tin-lead solder used in older pcbs (yours looks too recent for that, but perhaps wear gloves, avoid licking fingers.)

8-pin chip, I find TC1301BSSA, dual LDO voltage regulator for under-6v supply, the "SS" means each one contains a pair of 1.5V outputs, see SMD marking list found at https://smd.yooneed.one/code4253.html

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    \$\begingroup\$ I agree. special tools are needed to remove like a tiny hot air gun and metal vacuum pickup, then clean residue and parts then reattach or replace. \$\endgroup\$ Dec 25, 2020 at 7:54
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It got wet, for sure. While power was applied.

Clean with an old toothbrush and solvent or 99% isopropanol and inspect for corroded traces.

Try to fix the leak.

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It looks like a combination of corrosion and flux residue. Its possible that the board was not cleaned after some rework?

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